Unfortunately tanks are not used very often in all out war now because of their vulnerability, regardless of what your video game plays like. Reactive armour is all well and good, but any ATG missile can wipe out at least one or two per hit. The Wars in the Middle East aren't a good example of tank warfare at all, the Iraqi military was very poorly equipped compared to that of the Western powers.

I play a hell of a lot of World of Tanks (not suggesting that this is good evidence but the game is fairly accurate portrayal of 1920-1970 tank warfare), and where as I can tell you that LIGHT tanks certainly charge enemy gun lines and so to do mobile mediums, the tank destroyers and heavies will almost certainly lurk a little more and use their greater range to punish less concealed enemies. For example, a legion pattern basilisk/medusa/tank destroyer/wyvern/vindicator is not going to be firing on the move because that's inefficient to it's doctrine.

It would be one brave tank commander that charges a Tau gun line with hammerheads sniping.

Space Marines don't fight like tanks. They don't all run across fields firing at one single enemy. For instance, no tanks have ever been drop-podded into battle and none have jet packs (in the real world anyway). Devastators may be the closest thing, and they typically dig in. I think the similarities between Astartes and tanks ends with the thick plate armour and the .75 weapon. I think the tanks that aren't tanks of the 40k world are XV-88's.

Modern day MBT's have their equivalents in Space Marine Predators and Land Raiders. Better on the assault, vulnerable when sitting in one location and allowing themselves to be flanked.