"Google now has a significantly lower cost in standard compute instances"...without any commitments, prepayments, or restrictions. And RightScale's analysis excludes the additional 14%* savings you get from per-minute billing and never having to exactly guess right which machine type or region you'll need.
"14% extra, really?", you might ask. 14% is an estimate, of course, and YMMV -- see http://cloud.google.com/pricing
for more, including a TCO calculator where you can check our math and plug in your own assumptions. But it's not a contrived number: consider this simple example: suppose you're running some hadoop jobs that on average take 2 hours. On GCP you pay for exactly the minutes you use. AWS will round up to the next hour, so on average you'll overpay for 30 minutes, which is a +25% surcharge on the advertised VM rate.
On GCP, "pay only for what you use" means exactly that.