I think there are two different ideas and methods here. Official iPhone apps have to go through Apple and updates have to go through Apple.

Community developed Maemo apps (that aren't in Nokia or Ovi's repo) don't go through as draconian (as in one company or organization)and random process. Often the focus is more on functionality first, aestheics second. Take dialcentral for example, it's being updated frequently for functionality reasons (to deal with problems as they come up) and its aesthics haven't changed much from release to release and isn't likely to in the future. It may never be as pretty as it's Android or iPhone equivalents.

There's also several more reasons (money, don't care about apperance, etc..)but I won't go into much depth. So will you always see the graphical polish Apple look Apple loves from community developed apps? Probably not. Though I would expect more from Ovi Store apps.