There are few thoughts that come to mind:
1) D&D minis are relatively inexpensive, fairly sturdy, some are quite attractive and all of them are accurate per D&D (many sculpts being based directly on specific artwork). Metal miniatures, while not as widely available as in the past, still exist for the painter/modder to do his thing with. For visualizing purposes, it's very attractive to be able to put an actual beholder down against the player's avatars. We have quite a few Dwarven Forge and Hirst Arts pieces...not because we need them, but because they're FUN. It's cool to build a dungeon diorama, and cooler still to actually use your pieces with it. While it may not float some folk's boats, it's a lot of fun for us, sometimes.
2) Miniatures allow, in my game, for a better visualization of a combat experience. Sometimes this is unnecessary or more of a burden than a boon...when this occurs, we simply don't use them. However, during our last session, while playing a battle in a glass factory against some goblins (Pathfinder Adventure Path, btw), as the DM I was having trouble tracking the PCs relative positions and the 12 goblins locations within the room. Miniatures would have made it easier to run from that perspective. Even so, we had AoOs, move distances, bull rushes, charges, range increment determinations and other actions without using miniatures. No obscure house-ruling was required (though the bull-rush did require looking up the action on a battle-card). Miniatures don't involve trust issues, they're a handy reference tool.
3) The amount of combat or miniatures use has no bearing on our role-playing, neither it's quantity nor it's quality. A large part of role-playing, however, is generally beyond the scope of the rules. There are rules for skill resolution in D&D and tactical interaction, be it combat or social...but there are no rules for properly portraying your character a specific way...because there don't need to be. While we use miniatures as often as not, we have had combat-free social sessions fairly often or sessions where the combat is PART of the role-playing. But this is still a game of killing things and taking their stuff...and a lot of folks, such as myself, LIKE that.
4) 3e/3.5e has more consistent tactical options, but the insinuation that somehow previous editions didn't have equally focused tactical games or that they were somehow rare goes directly counter to my experiences. I remember players being very cautious about their movement, speeds and other details when in combat...moreso, in fact, than they would be in decades afterwards. I eventually discarded large portions of the initiative system, weapons speeds and goofy ranges, as they ended up being counter-productive to the AD&D games I was running. We spent too much time trying to understand and intepert the rules and not enough time playing. The biggest difference to me is that in 3.Xe, I've never had to do that. Although I hasten to point out that for some folks, that's where the fun is...in the tactical combat simulation. Clearly folks mileage varies on that, but enjoying a solid tactical battle does not preclude good roleplaying.