That's simply not true any longer. It just isn't. It's not "my personal experience". If you install ubuntu-restricted-extras, all of this is done transparently without ANY work on the users' part.
I would know, because I've never installed Flash manually on this system.
Yes, this is done transparently, and most people won't have a problem. As with most things Ubuntu, as long as you go with the defaults, everything will work smoothly.
What I'm saying, is that flash, java (plugin), and nspluginwrapper can be broken. It happens; and when it happens, it's not obvious what went wrong or how to fix it. Going 32-bit simply removes this support issue altogether.
I would know, because I've never installed Flash manually on this system.