On the preservation front, this might be the time to buy all the games on GOG if you haven't already. Sadly, they're not part of the GOG Summer Sale (possibly because Ubisoft knew this announcement was coming and didn't want to encourage people to buy the old versions?). The announcement doesn't say anything about whether the originals will also be pulled off GOG as well; considering GOG isn't getting the new games as far as we know, it seems like it might be possible you'll be able to buy the originals through GOG indefinitely, but I'm not holding my breath.
Back to the new versions: I guess since Steam only ever got Anno 1404 that it's fine that it's also the only one that gets a Steam version, but it's still kind of shitty. With Anno 1800 not making an appearance on Steam either I guess this isn't entirely unexpected. Setting the storefront issue aside, this is a neat thing that I wouldn't have expected, even with the higher profile Anno has nowadays. I never did get very far into the older Anno games (never mind the newer ones) so I'll be interested in picking up the whole collection at some point, if 1602/1503 are really that difficult to get running on modern PCs.