Yeah, no kidding.
Certainly not a valid reason, but rabid fanboyism springs to mind.
Its funny how these things play out. You have your rabid fanboys that can't take a joke, but then you also have those that like to stoke the fire, keep the arguments going, etc.
Its just a twitter joke that is meant to get a laugh and maybe tweak people.
And really, is there any question about the power brick on the 360 being nothing short of awful? That does not mean the console is awful. It also does not mean it is inferior in any way to the PS3. However the PSU is a monstrosity and a pain in the ass for anyone who tries to keep a tidy entertainment center such as myself. So a little humor about this fact is a big deal why?
I personally prefer an internal power brick just on the basis of looks, but then since my consoles are in a cabinet, I have yet to see the power bricks, so it has little impact on me.
As far as the humor part. I'm not sure why some can't take it easy, but this isn't exactly a new joke.
Of course some might say they find the one sided nature of these jokes to be tiring.