I think it's a different story with the original seasons. The intended version was 4 seasons, but Fox being Fox aired the episodes out of order, ending whenever they wanted and that's how 5 seasons came to be.

One might try to call it artistic privilege, but I don't think it holds when you're responsible only for distribution and not making.

I use MediaTracker which takes information form imdb and tmdb and it labels it as following:

• original series (seasons 1-5)
• Comedy Central (seasons 6 and 7)
• Hulu (season 8) with season 0 (specials) containing movies like Bender's Big Score