So? Space Marines have melta bombs for assaulting vehicles and melta weapons to fire at range (as well as the BS to be reliable with melta shots). Considering that powerfists can make you strength 10, making them pricey seems pretty reasonable.
None of this has anything to do with how effective or ineffective a powerfist is. Secondly, there are no powerfists with strength 10 in the space marine range, except perhaps for 13th company.
Space Marines already have good melta weaponry and lascannons, so the powerfists costing more shouldn't really be an issue.
And why wouldn't that be an issue? None of those weapons are effective in close combat. Powerfists are an extremely poor way to hunt tanks, about they only army powerfists can ever do any damage to is IG.
Considering that powerfists are, right now, pretty heavily overpowered and underpriced, Space Marine armies should be happy if that's their major issue to worry about. Look at the poor Tyranids: their most powerful gun can only glance, but glancing will no longer destroy a vehicle (save open-topped vehicles or skimmers). Plus, rending being downgraded takes a chunk out of the Tyranid armies fairly limited anti-tank effectiveness.
Perhaps you should read the rest of the rumors before jumping to conclusions. That said, nids have 2 guns which can be strength 10, of which one is glancing hits only, in 4th edition.
And wont be so in 5th.
And nidzillas don't have any trouble winning games.
Plus, how many players actually rely on powerfists to do most of the damage?
Any none blood angel space marine player as well as chaos, relies on the powerfist to kill the majority of the enemy. HQs are about the only model a space marine player wont give a powerfist too, who also has access to the space marine armory, for standard marines.
I've played against a bunch of Space Marine lists and powerfists just don't come up that much.
Then obvioulsy you have little understanding of what a competitive space marine list is.
The most horrifying use I've seen for them is the ridiculous new Biker Warboss + Biker Nobs + Pain Boy + Powerfists unit for the Orks. Cover saves, decent armor saves, Feels No Pain, invulnerable saves, multiple wound models, AND 15+ powerfist attacks on the assault. Unless they stupidly run into an ultra-CC squad with powerweapons, they're gonna wipe out pretty much everything they hit. I wouldn't be surprised if Games Workshop has that specific tactic in mind by nerfing the powerfist rules.
The bottom line is, space marines are getting double nerfed, a raised in point cost for powerfists, and one less attack with them. This will probably lead a lot of players to fielding other weapons. And will lead me to playing Dark Eldar - hopefully.