Technical Difficulties, Always the Same Servers, Why?

Pretty much the title. I watch the front page regularly and have seen the same 4 or 5 world servers have technical issues pretty frequently. I'm not starting this thread to fault SE's server maintenance, I just am wondering if there are any good reasons for it to always be the same servers. On Wutai my retainers have been in the same spot since...at least a week ago, maybe even since the last patch? Is it server population? Differing hardware? Ul'dah Markets reaching critical mass?

What do you all think?

Aww...my egg is gone. :(

I would hope it's not differing hardware. It would make logical sense to me that the same code on different machines should run on the same hardware if one expects the code to perform the same on all machines. In the maintenance description, the Ul'dah Market Wards appear to be a recurring theme.