Uhhh...

Do you guys honestly think that Twintania got to where she is today by being a weak little birdy that could be silenced or stunned?

NO - She worked HARD with her Shape-Ups on, a pink sports bra, and those p90x tapes to become immune to those things!

Seriously though, bosses are bad-asses because they can't be jerked around by your puny little Sleep spell, they laugh at your attempts to disable them because you are weak and they are strong.

The only thing you would be adding to an end-game encounter with status effects (like Virus, remember Virus chains?) is another scripted element (use slow at 44% exactly because he will do 6 auto-attacks that need to be slowed, use Heavy at 70% before the phase change so the tank can kite the mob and we can heal him before the big AE). AND if you could break the encounter with them, how would that be fun for you? They use some status effects in raids now, like getting heavy or bind on the Renaulds in T7, blinding certain bosses, slowing down the Dreadknights in T5, etc.

Lore-wise, it makes sense they are immune. Mechanics-wise, I think it would be much less fun if they weren't immune.