Has anyone noticed that extremely old users (going all the way back to 2004 for example) which have been abandoned for a long time have the same look? Brown spiky hair, black collared T-shirt, dark blue jeans and black "flat" shoes (what are they called?). Interestingly, I could not find a matching non-HC skin colour. I wonder why all these accounts are given such an appearance.

I believe it is because most of these accounts which you notice exist from the .com (USA) base of the merge, where accounts from .com were not replaced/removed yet recent Habbo updates have altered the clothing. Therefore they are given a general appearance even though the accounts will likely never be used again.

If I remember correctly, this has been occurring before the merge already.

Habbo clothing has changed though as well, with hotel updates and the switch from shockwave to flash.