The one tank strategy is the perfered method if you have a shield wearing tank class. The additional mitigation from block helps to smooth out some of the spikes in damage caused by multiple trons buffed at once or the tank debuffed by the cloud. Raids with Death Knight and Druid tanks however will generally find it better to double tank it, until such time as their tank starts to overgear it.
There are actually two reasons why single tanking the encounter makes it significantly easier.
The first as you pointed out is that everything comes from one location. So people with tunnel vision only staring in one place can see the mechanics coming from both bosses, instead of having a slime hit them from behind that they never even saw.
The second reason is because of the spikey nature of the boss damage in this encounter around when they gain a buff or the tank gains a debuff, healers have an easier time focusing their attention on a single target instead of bouncing back and forth between two. Because of the length of time it takes to cast larger heals on a target, needing to heal spike damage on multiple targets takes more time than on a single target (and in that time, someone could die).
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.