Nothing you quoted invalidates my point. PHB doesn't say it's not flammable, it has historically been flammable, and people don't follow/agree with Sage Advice. Simple as that. It's not a BG3/PHB difference, it's a BG3/Sage Advice difference.
Plus, if we followed the Sage Advice reasoning, there are a TON of things players and DMs pull that are "against the rules" because he's taking a 'only things clearly defined are allowed' stance in this instance when it's not taken in any other instance. Can a player recover caltrops? The PHB doesn't say they're "recoverable" so the Sage Advice logic says no but a practical application would be that of course a player could spend 5-10 minutes picking them up.
I changed my text to leave Grease more open ended. I'm going to test the spell soon, as it might just be that much more of a utility thing being flammable. Either way, this list of differences isn't to poo poo devs or to champion Rules Lawyers...it's just to give people a guide to things that might not be what they expect, and if something really sucks, we'll be honest about it.
I really appreciate you speaking up about Grease though, I've never seen anyone use it in a P&P game as flammable, but that doesn't mean that it wouldn't be a better spell for it.
This and some spells in general. I actually think they are going slightly off to be more realistic, and those providing immersion to the spells. A thing D&D doesn't do because it's up to the DM to decide.
Case in point firebolt having a smaller damage die, but causing things to burn. So it's 1d6 now vs. 1d10 a difference of a 1d4. It's a slight buff I've not seen any massive numbers off of burning normally within the 1d4 range. The flame also doesn't last long usually 2 rounds, which is 12 seconds D&D time. on average your still only getting 4 extra damage on an enemy. Since the burn doesnt stack, then your next firebolt will still only be 1d6 worth of damage. plus on average an extra 4.
If they simply stuck with a nongraphical games listing of spell effects then it would be boring. I know DM's that house rules things like using fire in a forest has a chance of starting a fire. It adds more realism, and consequences to the game. Makes you think, instead of going murder hobo all the time.
Yes sleep is way off.
So are spears = in game they are 2handed, in 5e they are versatile. It makes no sense that they are only 2handed in game, not even realistically.
Racial cantrips - are not according to 5e, most seem to have the same ones. could be place holder for future updates after bugs, and other things are done.
Passive perceptions are indeed automatic, they just show you. = When you spot a trap as your walking, spot a lever, secret door, etc. It's using your passive perception, since currently there is no way to have your characters actively looking. They simply use your passive perception for it, and it's always going.