Huh? Office will be recompiled to run natively on ARM, just like they showed at the CES. The "lack of legacy support" just means developers have to "do some work" (i.e. recompile and potentially deal with the same kind of compatibility issues as going from 32 -> 64 bit for example), just as Sinofsky said at the CES.
Remember who this is coming from: Intel, at their investors' meeting. Of course they're going to play up anything missing from the non-Intel versions. "Doesn't support legacy apps" can mean any number of things, in this case it just means the x86 binaries won't work, not that there's not legacy API support. (And fair enough, lack of binary compatibility is indeed a big deal on its own, but not unexpected.)