The A10's gun has no (declassified) rounds capable of piercing a tank's armor. Sorry I can't find a more reliable source but http://answers.yahoo.com/question/index?qid=20090812213536AA... Its anti-tank weapons are missiles.

I put "declassified" in there because I saw a video a few years ago that claimed to show an A10 ripping through a tank. No idea what those rounds were.

Perhaps not through the front armor of a current MBT, but that's not where the guns aims. Instead it hits the top of the turret, the engine deck, and treads. This may not always result in an explosive, turret tossing engagement, but it definitely will result in a mission kill.

Every video I've ever seen of the A-10 involved it doing nasty things to tanks with its gun, at the very least rendering the tank inoperative. From wiki, sounds like it uses 5:1 mix of ~1 pound AP and HE rounds.

Like greedo alluded to, MBT armor is usually concentrated in the front (and angled) to defeat rounds from other tanks fired from roughly on the level, they tend to skimp everywhere else, and especially on the top.

Yes but count in the time of the whole operation, I bet that equation looks a bit different.

Stuff like loiter times to find the tank, risk to pilots. I bet pilots are the most expensive component in the aircraft. Wikipedia says a helfire is $68,000 usd. Say you fit 8 on an aricraft, how many depleted uranium rounds must you have to take out 8 targets (and account for misses). That takes logistics to move, occupies room.

Oh, I thought they cost significantly more, not bad (much cheaper than an Abrahms)