I would be really shocked if Google charged for a service like this, it fits in with Docs and Gmail which have both always been free and have made storage space easier to fully use. If anything, they will profit off of it by people investing in even more storage with them.
in addition as time progresses the cost of storage has gone down and can be expected to continue to do so.
Docs and gmail let you slowly fill available space while being exposed to Google Ads. A Dropbox clone would let you fill available space quickly without ads.
That's a fair point. It does look like they have an in-browser UI though, and it will drive more traffic to Google in general. The Chrome browser is another desktop app that doesn't directly benefit their ad campaign, but they have put a lot of time into.
Gmail has POP3, IMAP and SMTP for free without ads.
Yes, and GMail for mobile is ad-free. On average, though, I would expect more storage+bandwidth costs per ad impression from a GDrive user than from a GMail user, if GDrive turns out to be similar to Dropbox.