"when those vendors decide that some application or API is end of life, you're screwed."
Google Reader for ex ? :)
Google Reader for ex ? :)
Microsoft is similar. Office 365 gives you something like 6 months to defer major releases. So say I customized something in SharePoint 2010 that doesn't translate well in 2013. Too bad -- I have 6 months to make changes or lose the customization.
It isn't always a bad thing either. Plenty of companies don't have or don't prioritize resources for platforms that they rely on. People still run Oracle 8 and Exchange 2003. "Letting the professionals" at a cloud provider handle it is a good thing, but it comes with a cost.