What i don't get is why i'm forced to be online to install the game even if i have the retail version...
Because when Larian sent the master DVD to the factory three or four weeks ago, they didn't say "well, that's our job done, let's go to the pub." they kept working on the game up to and past the day of release.
In my opinion, this is a good thing! I remember buying games in the 80's and 90's where bugs were simply never fixed. I don't want to go back to that model of sales.
That's not quite accurate. In the "old days", there was a deadline when the game had to be completed, and that day was the day it went "gold". That gold master was then sent for duplication and the boxing process. And (just as now) if you're lucky the developers made sure to work on a patch to fix any bugs discovered between that deadline and launch (which were often several weeks apart).
Fast forward to now, and that same deadline has moved within 24 hours of going live, with the gold master being just some incomplete version of the game that gets sent to duplication to get box production rolling. Why? Because developers know they can always fall back on patches for the weeks following launch (again, if you're lucky).
This not-so-newer way of doing things doesn't mean the game is in better shape by launch. In fact, if anything it's likely to be in worse shape because changes are being made right up until the last day with minimal time for testing, and that's one of the many reasons why today's games end up having more bugs than ever before.