Sure, and I'd expect any PaaS to have dynamic scaling. The question is, though, how many people really need a dynamic scaling PHP service? In your average web a

Sure, and I'd expect any PaaS to have dynamic scaling. The question is, though, how many people really need a dynamic scaling PHP service? In your average web app, you're far more likely to bottleneck in the database before the application requests queue (and the DB is significantly harder to horizontally scale), and if you do need more application CPU, it's generally as easy as "put multiple VMs behind a load balancer". You can even auto-scale with AWS using existing toolkits. Heroku made its mark because Rails deployment is (or was, anyhow) a lot of work if you don't know what you're doing, and they simplified it to as-easy-as-PHP deployment. PHP just doesn't have the same barrier to entry.