So... as MeeGo is RPM based, yet Harmattan/Maemo6 Qt-based apps can be installed on Maemo5 surely this means one of two things:

1) Nokia expect developers to package their apps twice, once as an RPM for M6 and again as a DEB for M5
or
2) Harmattan/Maemo6 is a purely DEB based OS with very little to do with MeeGo and it's RPM packaging system

Option 1) is simply an unreasonable expectation from Nokia of developers - it would be better for Nokia to ship an RPM based M6/MeeGo for N900 than expect developers to do double the work, this is the quickest way to make developers drop N900/M5 support.

Option 2) makes sense as Harmattan should be pretty well advanced, and means Harmattan/Maemo6 has nothing technically to do with MeeGo, although might be branded as such for the initial release, with a later release switching to RPM.

Assuming Option 2 is on the money, Maemo6 is MeeGo in name only... in which case yes, Fremantle/Maemo5 could be called MeeGo too! But that would be even more confusing, and highlight the fact it's a branding exercise only at this point rather than any major technical improvement/change.