I totally get that, and no markup above and beyond AWS pricing seems like the way to go.
But the problem is that AWS pricing itself is not completely transparent. It's based on usage, which means that the bill at the end of the month can end up being an unpleasant surprise, as it has been for lots and lots of AWS users over the years. Who can know in advance what their usage figures will be?
RAM-based pricing means that the bill at the end of the month literally cannot be a surprise. We have four available plans, and monthly bills map directly and seamlessly onto those plans.
We run on AWS (among others) but WE pay AWS, not our customers, because we think that part of the mission of PaaS is to shield customers from the many disparate pricing models on different IaaS providers. Want to run on Rackspace via AppFog? Same price. Want to run on HP? Same price. Azure? Same price.
PaaS needs to abstract hardware away completely, even monetarily. Paying IaaS providers directly is not the way to do that.
It seems we have different customer feedback. Our offerings are different, so we may be targeting different segments as well. What we get is that many of our customers (specially the bigger ones that run dozens / hundreds of machines) want to deal directly with the underlying vendor and do not want to be shielded from that. Having a predictable bill and dealing with a single vendor is convenient (specially when starting out) but the economics do not scale up as well for the customer as dealing with the IaaS vendor directly is always going to be cheaper, specially as they grow. It also moves the customer lock-in from the IaaS provider to your platform, which many customers are wary of. With BitNami, they can cancel the subscription and still keep managing their infrastructure through the regular AWS console or Rightscale. In any case, not arguing that a single, predictable bill is not appealing, just that it is not as appealing as what you would give up in exchange for that (at least for our current customer base, I am guessing yours is different in that respect)