Having worked on a system to handle international roaming I can tell you that it costs the mobile phone company almost nothing to run and relatively little to develop. Before the caps it used to be a huge winner in terms of € spent against € earned. After the caps it's still pretty good.
It's nice to see a government body doing something useful for once, but personally I'd like to see roaming charges abolished altogether (within the EU).
I don't suppose there's any chance of a UK body doing something helpful like this? Even abolishing the "unlimited" limited connection nonsense would be a start.