Why don't internet browsers use an online database for spellchecking?

I suppose this could be a GQ thread, so feel free to moderate, modulate, or modify this post’s location.

Inspired by this thread, why don’t internet browser spell checkers use an online database/dictionary for their word lists? That way, common names and recent additions to the lexicon could be correctly identified and spelled correctly across the internet. I think word processors could benefit from this functionality as well, but an internet browser should, by definition, have access to the internet. Firefox should be smart enough to know that the word “Obama” is spelled correctly.

But wouldn’t there be differences by locality? Such as “humour” versus " humor". I suppose a ping could find out where you are but if I was in America I would still prefer to use the spelling I am comfortable with.

The other thing of course would be where words are correct but the wrong word- such as “spelled” or spelt".

I use the Australian dictionary plugin for Firefox, so the spellchecking should work properly for my vocabulary. The same thing could still apply for an online spellcheck dictionary.

Lots of banner ads seem to know what zipcode I’m in, so I don’t think location is a problem.

That’s also a location thing (or could be).

The main problem with word processors checking spellings against the internet would be that they would regard as perfectly acceptable words such as “teh”, “definate”, “rediculous” and “OMFGLOLROFLMAOWTF???!!!”