What's the actual risk though? I have a feeling these users are also the more experienced and cautious ones, the ones with JS off by default, the ones who aren't going to be as easily tricked by social engineering, and that already removes 99% of the attack area.
"Large values in the HTTP Content-Length header can cause Opera to crash. Certain specific values can cause a memory corruption, which in some cases can allow arbitrary code to be injected and executed. In most cases Opera will just crash. To inject code, additional techniques will have to be employed."
More details in the pages linked to the URL I provided.
More experienced users are not safer in any way if they're using unpatched and unsupported software.
The vendors take shortcuts, and force UX on usera because they don't want to bother back porting security fixes or making security code separable from UX feature code