Let me elaborate on 'utterly horrifically critical' here. 'fork() fails due to the machine being a 64-bit box with 64Gb RAM yet running a 32-bit kernel and having run out of low memory' is not sufficiently critical: the database is still running, after a fashion, and that's what matters.
They're scared of going to 64-bit kernels no matter what the benefits because that's not what they currently have installed so 'stuff might break' (as if 'cannot fork()' is not breakage): 32->64, the kernels simply must be completely different, right? Have to retest everything.
This is not a rare attitude among people who run big production Oracle systems without really knowing what they're doing because they're Oracle DBAs at heart, who learnt to handle Solaris and have now been forced to Linux by the lower costs. Yes, you'd hope that everyone running big iron databases backing huge financial things with billions riding on them would have a sysadmin who understood the machine a bit as well as DBAs who understood the database: you'd be wrong.