The EU cap doesn't apply in-country, so operators would be free to charge whatever extortionate rates they felt like - as they already do for international calls.

Example: I've a UK SIM and a German SIM. If I'm in Germany and need to call the UK it's actually cheaper to do it with the roaming UK SIM, as that's price-capped to 30p/min or whatever, whereas the German operator charges nearly EUR2/min for overseas calls. That's FIVE times as expensive.

It's the same in reverse in the UK - I'm better off calling Germany using a German SIM. Bizarre...