I've asked the Romanian ccTLD why is that so, and their reply was: (sorry for the Google translation, didn't feel like translating this)
Currently we do not allow diacritics in domain names because there are two standards (alphabetically) for Romanian, ISO-8859-2 (tilde) and ISO-8856-16 (comma), Legacy and proper Romania keyboard Standard, and is impossible to work with two incompatible standards between them.
At this point ISO-8859-2 is depreciated with software makers obligation to provide support for ISO-8856-16. However, ISO-8859-2 is currently used in more than 90% and
expected to decrease below 50%. We can not predict at this time, but when most will use the correct character set will Romanian IDN domains allows registering the subset latin2.
I've asked myself how many countries in Europe allow national characters in their Internet domain names, this was after I've found out that starting with 10th of December 2009 the European Union (.eu) registrar offered support for all official EU languages.
After a bit of research I've come up with this map of Europe. Green is for Countries that allow national characters in domain names, Pink for those which allow only the American Standard Code for Information Interchange (US-ASCII) characters.
I've took some notes which can be found here.
I've learned that European Union (.eu) and Slovenian (.si) registrars allow domain names with proper (comma) Romanian characters, while the German (.de) and Moldavian (.md) registrars allow domain names with the deprecated (cedilla) Romanian characters.
The last registrar to allow Internationalized Domain Names (IDNs) was the Estonian ccTLD:
Starting from June 13, 2011 the Estonian Internet Foundation will bring letters with diacritical marks õ, ä, ö, ü, š and ž to national domains ending with the suffix .ee, which means that the .ee domain will be covered with the full range of the Estonian alphabet. The Estonian Internet Foundation in cooperation with the Association of the Estonian Patent Attorneys has introduced a period for reservation of .ee domain names containing letters with diacritical marks before commencement of general registration of such domain names.
The sad part is that the Romanian registrar announced on 15th of June 2008 that they've updated their system, the interesting part was at 11. (again sorry for the Google translation):
11. The new system is ready to allow the registration of domain names with diacritics in Romanian. But these services will be provided in a later stage once they have established and accepted rules of domain registration with diacritics.
Next time you pay for your domain name, don't forget to ask them about how long it will take to establish the rules of domain registration with diacritics. It's been more than three years since they announce it.
P.S. One might think that the reason that the Romanian ccTLD doesn't allow the Romanian special characters could be the fact that it waits after ICANN to approve the Romanian characters. This is not the case, as you can see here signed by the hand of the «Head of .RO Registration Services», because of "NOT BEING ELIGIBLE FOR FAST TRACK. The Romanian diacritics are included in the Latin script".
A Romanian version of this post was published in Kamikaze Online.