Oh wow... I didn't know Google lacks the ability for customers to specify reverse DNS. I had assumed any full-service cloud provider would offer this feature.
If Google doesn't have configurable RDNS, they're not a "one-stop shop" for all hosting needs. For example, a customer wouldn't send transactional e-mails from a server at Google because the lack of RDNS would affect deliverability.
We are most definitely not a one-stop shop yet. We don't even have IPv6 on GCE (I recommend Linode for low traffic IPv6 to IPv4 bridges).
Moreover, (sadly) your example doesn't hold anyway: sending email is actually something all cloud providers try to avoid (SoftLayer in Brazil lately is the notable exception). So getting anyone to whitelist your smtp and other ports is usually an unpleasant experience.
Oh, this actually works great at AWS, yeah! We've been sending transactional e-mails from our servers at Amazon for a couple of years. They do require you to request the e-mail ports be unblocked, but once we made the request it was approved within 24 hours. As a bonus, the same request form also has a space where you tell them what you want your reverse DNS to be. Very handy.
Last year Microsoft also announced Azure support for reverse DNS entries. So I would anticipate Google getting on this "bandwagon" fairly soon too. Just my guess though!
If Google doesn't have configurable RDNS, they're not a "one-stop shop" for all hosting needs. For example, a customer wouldn't send transactional e-mails from a server at Google because the lack of RDNS would affect deliverability.