Umm...have you actually played the last two Fallout games?
Because everything you just said actually describes them perfectly.
And there were certainly limits on what you could do in the original Interplay Fallout games, contrary to what you seem to think. They certainly weren't some open-world sandbox paradise by any means.
Bethesda "dumbing down" their games for the filthy casuals?
Yawn.
That false chestnut was old back way in 2006. Move along.
As someone who purchased the original Interplay/Black Isle Fallout titles either on launch day or within a week or so thereafter...trust me, I'm not.
And as someone who is also a Fallout 3 and New Vegas fan, even less so.