High fixed costs can often be a factor. Google now has about a hundred thousand engineers, right? If you make a great ad network (and found way to make it scale without needing google-scale servers) google wouldn't be able to compete on price.
That's also why MS won't shift push a basic subset of HTML as a document format (using Word as something you use to lay out printing), leaving things like MediaWiki as the bees knees of collaborative editing.
That's also why MS won't shift push a basic subset of HTML as a document format (using Word as something you use to lay out printing), leaving things like MediaWiki as the bees knees of collaborative editing.