Well, I run FreeRunner with Debian and it surely is a standard distribution. The only package not from Debian main repository is the kernel, since there are still a few Neo FreeRunner drivers not in Linus' tree.
Of course, the point was "shipping". OpenEmbedded (based) is not maybe a standard, though it is quite popular in various embedded devices including Palm Pre phone. It could also have been pointing a finger at the faults of the shipping software compared to eg. Stable Hybrid Release (SHR), but it is a working phone out of the box.
And finally, one could argue if maemo is a distribution or a glorified SDK. I think not all deb:s are installable from a public repository with source code where available, so it's not that trivial to build one's package selection from scratch? Please correct if I'm wrong, ie. is the delta between Maemo and Mer ("maemo reconstructed) really small or not. Mer seems like a real distribution.
But whatever the case, Nokia N900 is by far the best mass-market choice to recommend to others if one wants to somehow advance open source mobile stuff. Maybe in a year or two it will run on standard Debian as well without losing any features.
[ending with obligatory mention about Nokia's open^H^H^H^H"proprietary" Ogg family media formats support]