I guess you came from the US. The same can happen to Europeans going there.
Since 2010 European mobile carriers are required to ask permission to go over 50 EUR ($70) per trip outside the home area of the subscriber. That avoids the "bill shock", but telecoms were not happy about the rule.
The EU can't do anything about US carriers. My advice is to get a special international plan or another SIM card for Europe. I have a US number, a UK number and my local number in Barcelona.
I'm from Oz actually, but the issues are the same. I agree there isn't much the Europeans can do on this buy themselves, but there are so many international agreements on trade signed each year, I don't see why this can't be tabled as a restrictive trade practice.
I got one of those special deals for travel but they are ridiculous too. From now on (and until the magical international agreement is sighned) I am simply buying a prepaid SIM for each country too. Still that means that no one can call me on my "home No."
Maybe one of these dual SIM phones is the answer for travelling. I'm not sure if it works but I imagine it should respond to both No.s
"Today [April 3rd] the European Parliament voted to end roaming charges by Christmas 2015, as part of a wider vote in support to the Commission's proposed regulation for a "Connected Continent" (telecoms single market)"
EU member states will now review the regulation and the commission hopes to get final agreement by the end of 2014.
In addition to roaming, spectrum and consumer measures, the package contains proposals on net neutrality. The parliament put forward amendments for stricter rules on net neutrality, particularly around so-called specialised services.