We already do, including Nokia and third-party (maps, flash, skype & gizmo installers) packages in the stock firmware and packages available elsewhere (garnet, boingo, hava player, rhapsody etc).

From a purely practical point of view, yes I mind (particularly the first category, no one is forced to use the rest or keep them installed to avoid breaking updates) because invariably they get far fewer fixes than the open ones.

However, openness and price are orthogonal, and such an app store doesn't necessarily imply closed-source (leaving aside the GPL implications of certain fruity store & SDK terms). I suspect a lot of current maemo users, myself included, wouldn't mind paying for F/OS packages (and other things being equal would even prefer them to closed alternatives) and the larger "consumer" audience wouldn't know the difference.