Given there so little consistency between games (not that there's a lot that's been impacted anyways) and regions it's hard to guess at, but it doesn't sound like an intentional thing unless more games get impacted.
Yeah, so, I checked myself and the .xml served for one of the games that isn't updating correctly both serves current version data and has a working update .pkg url from the CDN. I can download it on my PC perfectly fine. It seems to be an issue with the PS3 OS specifically?
You could theoretically download the .pkg and move it to a flash drive to install on the PS3 manually, if you've already installed CFW to do that.