Indeed PaaS is an extremely tough market with tons of external competitive pressures. Right now there are two major strategies. The first is the notion of a 'polyglot' platform (Heroku, DotCloud, CloudFoundry) which is multiple languages/databases. The second, and our strategy, is focusing exclusively on a stack (node for us) and building tools and systems which work exclusively for the stack. Essentially, I believe it comes down to company resources which strategy to choose. When Heroku started they focused exclusively on Rails, and did it really well. Not until recently after growing the team and dominating the rails hosting market, did they make the huge shift to polyglot.
Finally, recently, there is a new emerging strategy which I am really excited about, which is even more focused. Real-time javascript frameworks, with hosting bundled into the platform. Examples of this are Meteor and FireBase. Certainly there is some preliminary evidence, that these may be the future.