They're two different versions.

[Symbian] Ovi Maps 3 = 3rd version or iteration of Ovi Maps for Symbian.

[Maemo] Ovi Maps = 1st version or iteration of Ovi Maps for Maemo.

The maps themselves should be the same, the difference is in how long the product has been in development.

Though I'm willing to be that with Nokia's QT plans there will be no seperate Ovi Maps in the future.

Just QT Ovi Maps that's cross-compatible with Meego, Symbian 3, and hopefully Maemo.