You make great points. Not having bought the game yet, I trust your synthesis. Still, the point I was making seems valid: "Role-playing impossible" is impossible. You can roleplay your way out of (almost) ANY pigeon-hole. If you want to role-play a 19 year old who is a non-veteran and has no spouse or child, obviously it is going to feel very awkward in FO4. I hear ya on that one.
But are any of those constraints that 'significant?' Does being advlt, having a kid, and a spouse really LIMIT what you can make your character into without breaching your suspension of disbelief? Maybe you are like the Buddha, and decide to turn your back on your past life at the age of 30 and leave your wife, kids and palace behind!
It does sound like the developers put the player character into a bit deeper and steeper pigeon-hole this time around. I imagine they did so intentionally, and I don't think they did it to "squelch roleplaying." In fact, they may well have done it to FACILITATE roleplaying.
Some folks need a bit of grist for the mill when it comes to roleplaying. I have DMed plenty of RPGs where at first, people had a very hard time knowing what they would like to do or be in the game. They depended on me or other players with more knowledge of the game world to give them some pointers. Maybe the developers felt that roleplaying would be EASIER for folks who were less adept at it if they slate were a bit less blank?
Certainly a completely blank slate is not what anyone would want, as that would amount to: "here is your IDE, a copy of Notepad++ and your C++ and ActiveX textbooks. Make your own game!"