Agreed on the definition of exploration - although knowing where you are and where you're going doesn't invalidate "exploration" in my opinion. That doesn't mean you know WHAT you will find

To put it simply, exploration as I see it is more a matter of [i]what[i] than a matter of [i]where[i]. ( well it's obviously a matter of "where" to, as "exploration" mostly refers to points in space, unless you're exploring your inner self... Am I getting sidetracked here? Yes, I am ).
An unfamiliar place isn't necessary uncharted, but it's still fog of war. In a TES game, you have a map, but that absolutely makes sense as the lands you're doing your adventuring in has been inhabited for centuries, even millenias. That doesn't mean there aren't any treasures left to find, dangers to be battled, etc...
In a TES game ( let's consider oblivion and skyrim since they changed the rules by introducing autoscaling ), I still find danger. Mostly because I'm playing at the highest difficulty setting and my level 50 character can STILL be one-shot by mages, vampires, or *ancient* dragons. But I think it's a bit unfair to say you can't find hard to reach secrets or places. By wandering off the beaten path, you can find lots of ruins, tombs, caves, which may or may not hold valuable things. Getting lost, though, I admit, isn't in the menu. Dungeons are mostly small ( especially compared to Daggerfall ! Boy you COUL get lost back then ), and you've got the compass. Luckily, it's de-activable.
I'm more torn on the topic of temporary inaccessible areas. There are some in Skyrim actually, places you can't go before completing a task and ( basic example ) being provided the key. One could argue that you should be able to pick the lock, and I'd agree. But then again, there are RPGs ( like MMX, and to some extent DOS ) that completely prevent you to actually keep going in the world unless you followed the main storyline and unlocked entire areas. In MMX this is done using the two hard ways : High level monsters preventing you to progress in an undiscovered zone because they simply tear you to shreds, and needing "blessings" to walk on water, jump on mountains, etc ( metroidvania style ). In DOS, so far, it's only high level monster, which you can't beat unless you did some XP to gain levels, which you can't grind because there is no respawn.
So here are my views on full and half open worlds. They both bring something to the table, and while a full open world will put the accent on being able to go wherever you please and discover things emphasizing the "discovering" part of the "exploration", half-open worlds will put more restrictions and maybe feel more organic, emphasizing the "dangerous" part of the exploration. It's all a matter of preferences, in the end. I can live with both!
And about re-playability : sure, I get your point. A game that you will sometimes bring back ( or not even delete ) to play again, because it's not a finite experience. In that regard I hated the latest Xcom, which I didn't even finish, because I felt that it actually was a finite experience ( and well, not even finishing it, I'm not gonna replay it :p ), but I can relate that to a good old Civilization. Those games never leave my harddrive, because I often feel, like, a NEED to replay them !
But again, taking Skyrim as an example : I never uninstalled Skyrim since it went out in 2011. I still like playing it, the exact same way I like re-playing a Civ game. I just resume my character's adventures, play for a while, mod a while, and when the rush has passed, I put it to sleep again. Isn't that another kind of replayability ? Such a huge content and dedicated community that, well, you just never reach the end of it ? And I don't even have the addons!
As for consequences : funny enough, Skyrim is probably the first ES game to feature some real decisions, especially when it comes to allying with the stormcloacks or the empire. You can also either join or hunt the Dark Brotherhood. The Daedras' dilemmas : will you be a complete *ss or will you walk away. Part of the reason I see Skyrim as a real RPG is because choices and consequences really matter to *you*. You have to play your role, feel it, and feel bad when you do something bad. If you don't, and play Skyrim like you'd play a GTA game, sure, it's not a real RPG, just a big, uninteresting world. But let's not forget the whole story is a consequence to the world of Tamriel, that will be discussed in the next game, featured in new books, etc.
As far as modern RPGs goes, though, I think Fallout New Vegas is the open-world game that got the whole choices/consequences thing the most right. Not only were YOU feeling like sh!t doing some not-very-glorious things, but they would come back to bite you later on. The way you dealt with factions have a consequence on the ending, choices you make along the way too.
Okay, that's a big Wall of Text. I get carried away easily, it seems !
Basically, I'm just politely disagreeing with some of your points, but again I guess this is a matter of past experiences, what we grew up with. So don't feel threatened or insulted, this is merely an exchange of opinions :p