Actually, I run the studio these days, I'm not an engineer "on the front line", but tend to give replies that give a general drift of the situation.
For Worms PSP and infrastructure mode it was as simple as this is in europe - the libraries and support code to deliver what some of you expected simply wasn't there when we needed it to be.
We've had enough problems supporting some features of Lemmings (regarding user levels) never mind infrastructure mode in Worms - and Lemmings is a SCEE product where we've worked with them extremely closely.
We got there in the end with Lemmings, but for Worms we were on a very tight deadline and adding Infrastructure mode play for Worms would have taken us way beyond that - and unless our publisher makes that call, it doesn't go in.
For the record, both Lemmings & Worms are now "gold" (for want of a better phrase, given UMD media) although both are now in submission/test at SCEE (awaiting approval) before their release in the Spring.
For DS, the same situation was present, i.e. lack of usable libraries and actual methodology via Nintendo at the time of development (the DS version is in final throes before submission too). I know Mario Kart has wireless, but the small point of this being driven by Nintendo (and all the support that musters) should be enough information as to why we didnt' have it.