Why do I want to say "the iPhone" instead of just "iPhone"?

Apple is somewhat notorious for omitting articles when talking about their products, and statements such as "People love iPhone" hit my ear a little strangely. But when I stopped to think about it, I realized that I wouldn't say "the Windows" or "the iWork".

I couldn't come up with a reason that I use the definite article before some product names and not others. Is there some sort of convention (probably not a hard-and-fast rule) for usage here?

I think we instinctively use determiners with countable things and omit them with non-countable things. "Windows" or "iOS" or "time" (the concept) are not countable, but "iPhone" and "PC" and "schedule" are. So we install run Windows on the PC and use iOS on the iPhone and report time on the schedule, but we do not run the Windows on PC or manage the time on schedule.

Edit (per comments): this is all for singular objects. If you use the plural (e.g. "iPhones") then it's natural to omit the determiner; in fact, if you said "the iPhones" then you would almost certainly be talking about either specific phones or various iPhone models (3 and 4 and 4S...).

Like in man vs. Man: iPhone is an iPhone, any iPhone. The iPhone is the product family as an entity.

You buy an iPhone. The iPhone outsells most of the competition.

There's probably no Apple's artifact there. It's just incidental that the product family is so named with the generic name as part of the brandname. Say, in contrast to Android phones: they are not aPhones or something like that.