This is all so silly!!
Surely BioWare have stats on how many players actually use heavy weapons and/or how often they use them.
I'm assuming that once the average player has played ME2 enough, they will become proficient enough with the myriad other weapons and skills available to them, that heavy weapons (apart from maybe the Collector Particle Beam) will be all but useless.
I've played ME2 at least a dozen times through, and in that time I've fired the Cain about 4 times - mainly to see what it was like. As has been said before, heavy weapon ammo is very rare - as are the opportunities that players might actually need to use it.
I'd want the Terminus gear for completion's sake, but the benefits imparted by modular armour and the skillful use of other weapons and abilities, outweigh any practical use for it on a 'real man's' difficulty level.
As for 360/PC users being left out in the cold, well that's just the way it is. The company I work for regularly offers incentives to entice new customers into the fold. It's just the nature of the beast when you're in business. I've said one or two (or a few things) against BioWare in the past (even quite recently), but you have to cut them some slack - they're trying to push an old product into a new market. Not an easy feat for the best of companies.
Time and life move on, and eventually people relegate little blips like this to the 'I don't actually care' basket. Heck - I did about 10 minutes after reading the first news item on this.