he/she means you can probably get away with just adding more dynos or whatever to your PaaS to get the performance you need, because the costs of moving out will be significantly higher (opportunity costs and time spent)

eventually if you're spending thousands per month on a PaaS it might be time to reconsider

A) you can't

B) Nothing in particular

It's not about the application or any technical concerns. It's purely a business decision - above $25k a month you have room to hire people and still save money, below that you really strictly do not.