Back when PC FPS games went from having long single player campaigns plus multiplayer(Duke Nukem, Quake, Unreal)to multiplayer only for the same price (Quake 3, Unreal Tournament) I thought it was a rip off. The Battlefield series was the only exception where the multiplayer content seemed so extensive that it justified the cost.

I didn't feel that way at all. Quake 3, UT and Tribes all had very comprehensive multiplayer, far more than the MP components included with previous SP iterations (if any). As such, I've never really been compelled by multiplayer that was included with a single-player game. It's always felt tacked on and lacking in depth.

Or for a more recent example, look at the failure of Unreal Tournament 3 on consoles compared to the success of Gears of War. Certainly the lack of a true single player component in the former had a lot to do with that.

That's not really a good example at all. UT3 was a failure in all regards. It didn't please fans of UT2004 and it didn't please anyone else. The lack of a proper single-player campaign had nothing to do with it. As for GoW, it's a much more casual game than UT. It's also much more playable with gamepads. It's not surprising that the series has done so well on consoles.

A better example of how SP components don't really matter in multiplayer games is Tribes: Vengeance. Irrational put a lot of effort into the SP campaign and it was actually half-decent. Unfortunately, it was not representative of multiplayer gameplay at all and the multiplayer itself felt somewhat half-assed, no doubt a result of the split focus between MP and SP. Unsurprisingly, T:V was the worst-selling game in the series.

It's probably the first military themed FPS campaign that I've looked forward to playing since the original Call of Duty.

Wait, what? The BF3 SP campaign looks just as derivative and uninspired as all the CoD campaigns made in the past 6 years. Completely linear, completely scripted, follow NPCs and wait for them to open doors, formulaic sniping/stealth/rail segments, etc. Literally nothing unique or ambitious about it whatsoever. Hell, the last Operation Flashpoint SP campaign was more interesting.