Earlier quoted context omitted.
Well I wouldn't say they have only a single line of business. Yes, they make pretty much all of their profits from advertising. However they no longer just do searches. They do email, file hosting etc. You name it and they probably do it. They do make money from ways other than advertising too. They have quite a few pay to use services. Like business emails or Google Drive.
and yet none of them make money except search advertising. it's almost all of their revenue on a percentage basis. edit: i do believe they make a bit of money with youtube now, but it is still advertising. they haven't successfully SOLD anything to date.
I actually think lots of them make money -- over $5 billion in non-advertising revenue in 2013 [1]-- its just they are dwarfed by the scale of the revenue from search advertising ($50 billion in 2013.)
> they haven't successfully SOLD anything to date.
If they haven't sold anything but advertising, they must have just conjured that $5 billion in non-advertising revenue (and that total, and the proportion of non-advertising revenue to total revenue -- has been growing every year) in 2013 out of thin air. Which, you know, would be even more impressive than selling stuff.