Is there some other huge open world sandbox RPG engine with less bugs than Skyrim and Fallout New Vegas?
With no mods installed, neither Skyrim nor New Vegas ever crashed to desktop on me. In contrast, there are smaller, linear games (which are much easier to QA) that have crashed. The only bugs I encountered in either game were insignificant glitches, like a radscorpion melting into the terrain, an NPC in Riften stayed in jail even though he was supposed to be out in a few days, Louis Letrush cloned himself, a skill magazine was melting into the terrain, etc. Personally I don't care about that type of stuff.
It's one thing to QA a linear corridor shooter with 5-10 hour campaign hundreds of times, but it's not possible to test these big open world sandbox RPGs in the same way. You could hire a staff of hundreds to test the game nonstop for years and still not find everything. And when you do find something, you have to determine whether fixing it could result in problems in other areas.
If you enjoy this kind of big open world sandbox RPG with hundreds of locations and quests and thousands of NPCs, etc., some minor glitches come with the territory. In both Fallout New Vegas and Skyrim, they managed to catch and fix (at least for the PC version) any serious, gamebreaking stuff prior to release, that's what counts IMO.