There's no point in comparing the Playstation 2 online service and the Xbox Live service when talking about the Playstation 3 online service, because according to Sony's press statement, the new online service will have a centralized hub (just like Live), it just won't be as controlled by Sony as the Live service is by Microsoft. Developers will get much more power over their respective online games in the Sony system. Microsoft are actually having problems getting MMORPG's developed for their consoles because of their extremely strict (and probably greedy, if I know Microsoft right) rules for usage of their Live service.
Of course, until we get to experience Sony's new online service, this is all speculation and Sony hype.
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Like I said just look at PS2's current online system and you'll have an idea of PS3's online system. Pitty isn't it?