Portal as a separate title on its Steam digital distribution service, gamers might have been confused as to why the developer didn't pursue a similar avenue with the game on Xbox 360, via the Xbox Live Arcade service. As it turns out, it did, but the title was rejected due to size limitations and other unnamed reasons.
GamesIndustry.biz reports that during Portal's development, Valve did approach Microsoft to make the title available through XBLA, but several factors made the title an undesirable candidate for the service. Still, marketing director Doug Lombardi does state that the company is always happy to renegotiate. Maybe we'll see Portal on XBLA one day, after all.