Do you mean differences between wizard and sorc, or between mages and others? If the latter, then I think reducing that difference is the intention. I could go into a variety of reasons why that's a good idea.
If the former, then I think the fact that DDO's wizards and sorcs cannot qualify for the same list of specialties (like they can in D&D) provides an easy way for the devs to avoid making them very similar, since they're not presenting the same options to both.
That brings up a perverse, but unlikely, possible outcome: sorcerers of a certain elemental spec will have less spells of that element than other sorcs. Fire spec won't learn scorching ray or anything they can free-cast. But there are several ways Turbine can avoid that (such as simply giving Fire Savant knowledge of BH, Scorch, and FB as part of the specialty, freeing his slots to learn something else).
Yes, although they'd have to come up with new spells because there's only 2 low-level-ish acid or lightning and 1 low-level cold.
I think that'd only be a problem for bad players. If you've learned that mini-fireball does the damage of two sword swings, you let someone slash it 3 times and then you can open up. Caster players really already know how to avoid pulling aggro.
That's possible for generic D&D casters with the Energy Substitution feat, so I think that if Turbine wanted energy-type swapping they could provide it without waiting for specialties.
Spellpoints are the replacement for spell slots... there's nothing surprising about that. If the DDO archmage had cost spell slots, it would've been both more expensive for the player, and more work for the developers.
The D&D rules for elemental savant has no kind of precedence to give up spell slots, as Archmage does. That means they almost absolutely won't have to make any payment beyond qualifying for the specialty.