Piro's name on the door is in hiragana, which isn't used for foreign words and names.

Piro speaks:
Ok, first off. 'piro' is, as noted, taken from the game 'kanon'. In the game, and in the art books, piro is spelled with Hirigana, not katakana.
Secondly, since piro put the name on the door himself, and since he is an american, not japanese, don't expect him to follow any 'rules' - also, even tho there may be standard, typical, and most often seen ways of doing things, there are allways ALLWAYS exceptions. I have seen japanese names spelled in katakana, hirigana and kanji. I've seen english names spelled in hirigana AND katakana.
Like any language, sometimes you bend the rules for desired 'visual' effect. Koge Donbo is a japanese name of sorts (i assume it is a pen name) but she spells it in Katakana. Note that 'Megatokyo' is spelled in katakana - that is because i was told it looks 'odd' in kanji - and that sounding it out in katakana makes more sense.

-chan = suffix used for children, people younger than you, or close friends.
Wai = Yay