Stealing anything is illegal..

But is it punishable by law? Then its a big NO for you.
Illegal is unlawful. For something to be illegal it has to be specified in written law. Most countries don't have a policy on bitcoin, so stealing it isn't illegal.
Well, that statement just sucked 50 IQ points off everyone.
Most countries don't have a policy on tiddlywinks, either. However, stealing a kid's tiddlywinks is still theft. Punishable by law. As is stealing Bitcoins. Whether or not specifically addressed by proper name in the text of the law.
No one will investigate the theft of Diablo 3 gold or WoW gold. In fact, even Blizzard support will not do anything, not to mention the police. So yes, in most countries(which did not recognize Bitcoin as currency or property), stealing bitcoins isn't illegal...