In the case of the delisted Sega titles being available to those who bought them before they were replaced by newer releases, I think it's mostly down to the fact that they weren't delisted due to licenses expiring. Outrun 2 Online Arcade, After Burner Climax, Sega Rally Online Arcade, and others all had various manufacturer licensing attached from Ferrari, Northrop Grumman, Boeing, Lockheed Martin, Toyota, Ford, Subaru, and others. Sonic, Golden Axe, and many other iconic Sega games are wholly owned by Sega with no other IP under license used within them, so it makes more sense that they could be freely available while the others remained locked to the original hardware platform for owners who had bought them prior to delisting, but I'd love to be wrong and have all of those to play on X1. Perhaps it's just down to prioritization due to what can and cannot be sold in stores now.
In any case, I wish Sega would just go in and scrub out, alter, and otherwise eliminate the offending models and references to those third party IP and re-release those games as 99.9% owners surely wouldn't care just as long as they could continue to play them today without limitation. Sega has quite a few great titles just sitting there waiting to be sold and played by people today and they choose to do nothing. Disappointing.
On another note, L4D2 needs more updates to its performance as I've run into so many instances of slideshow moments during more intense areas, particularly with the Hard Rain campaign.