But to answer you new(ish) questions - T2 UE only works on players with a decent RAM cache, play it back on (for example ) a DVL700 and it pauses at the branches.
On my linn DVD player, Robocop (Region2) is completely seamless. If you want my definition of seamless, then it is that it branches with no pauses, and is completely imperceptible. I edit video and film for a living, trust me, if there is the tiniest stutter, I notice it.
On some players seamless branching titles pause, on most current ones they don't. MGM apparently didn't implement it well on a lot of their titles. In general MGM don't have much of a track record for quality on DVD so it doesn't surprise me. Perhaps the R4 Robocop doesn't branch properly, I couldn't say as I don't have it.
I'm not sure what your obsession with MGM is? Most of the major studios have had some crpaulent DVD releases (look at Warner's ultra lazy R4 release of Logan's Run, the bloody thing is R4, but still in NTSC!). You need to understand that just because a big bux studio does something in a crappy way, it doesn't mean that you can't do better on a humble PC.
If you need proof of that, just look at the current DVD release of the Star Wars trilogy
Any of us here with half a brain can do a better job on fixing the matte lines, the sabres etc. and the colour grading is off in a lot of places.But to answer your question, yes, the software tools I mentioned do seamless branching. They do it just as well as T2 and stargate, they use the same method (Have a look at the streams if you don't believe me, in fact have a look at the Robocop R2 streams, you will se that they use the same method also).
So just to make sure it is clear. You can do seamless branching on a 'home computer', and you can do it with more ease if you are running a Mac. And it is seamless, as in seamless.