Being a prisoner is quite restrictive: I have to invent a reason for having been arrested. That's different even from an ostensibly more involved origin ala BG1 (where in theory had a lengthy life at Candlekeep, and your BG1 "information" page had a basic outline of a background for you). Even so, I find this "you grew up in x" but otherwise we are staying vague about it (which NWN2 also used) is an acceptable approach to a set starting point. DA:O's origins, IMO, are better.
But something that requires a particular act - being arrested and convicted, however that happens - I very much dislike. It requires a lot of mental gymnastics to justify.
In Skyrim I found it very easy. It's a border crossing during a civil war. It could be that anyone trying to cross there at that time was simply deemed guilty by association. Maybe there's an approved list of travellers, and you're not on it, and anyone crossing the border without permission is automatically deemed a traitor.
The best part about how Skyrim handles this is that the PC isn't even ever expected to know why he was arrested, so it doesn't need to be a significant part of the backstory. It's just a significant part of that day.
Oblivion, on the other hand, was a mess. The main plot hook is provided by the guy who imprisoned you, and you're given the opportunity to ask why you've been imprisoned, a question he reruses to answer. So, given that you've been imprisoned, might not have any idea why, and the guy who did it won't tell you, why would you trust him and do as he says? And yet, that's exactly what you have to do if you're ever going to see the main quest.
The reason I like Skyrim's starting point is the same reason I like NWN's and KotOR's. All you're given is a location, with any background beyond that or motive for being there left entirely up to you.