I just don't think health packs would work as well in games with cover systems... The whole mechanic is basically having onslaughts of enemies, with perfect accuracy, so you can only duck out every now and then for perfect shots. One hit, and you have to quickly get back behind cover before you die.... Hide behind cover too long, and they flank you. Theres your strategy...
I agree with you in regards to MW, but I would rather a cover system in those games ala Vegas 2 LONG before I wanted health packs. If you think back to those health pack games, the enemies were no where near as ruthless as they are in games like Gears or classic FPS, otherwise, with no cover system and health regen, and you just standing out in the open in front of enemies, you'd get gunned down.
Also, sure the Regen thing is a bit of poetic justice, but it's still a helluva lot more realistic than health packs... Health pack games, you can have like whole magazines fired into you before you die. Regen games, 3 shots, or one head shot and you're dead.