The new Canon XTi CR2 format is not "recognized" by LR. So it's not cut & dry. No new owners of the XTi can use the beta version until Adobe adds Canon's format. Interesting, Mac's Aperature has already adopted the new CR2.
Well have you imported a file into Aperture from the 400D yet?
The CR2 format has been around a long time. And Lightroom does support it. If you were specific about the 400D, then you are refering to new RAW, rather than a new file type.
The 400D is a new camera, barely 2 weeks old and even the version of DPP that supports is not publicly available. Beta 3 is how old now? Beta will support the 400D and even the Nikon D80, before ACR 3.6 will.