Yes, I agree 100% percent.

When I worked for a large building automation company, we moved one of our tools to Microsoft Azure. It was a foregone conclusion that we'd use Azure, because of the strong working relationship we had with Microsoft. However, that didn't ease my concerns over vendor lock-in.

IaaS solutions are probably the best bet at this point, for those really concerned about vendor lock-in. Although, I'd hazard to bet there would still be issues moving between vendors.

When you go the PaaS route, you're really buying in to the platform. Which at this point is pretty strongly tied to the vendor. Even if multiple vendors offered the same platform, you'd still be tied to whatever platform you targeted. So, you'd still have platform lock-in. Of course, that's an issue we had long before the current cloud platforms.