I’ve seen verbiage on this echoing around the Net while the various Cloudy festivities go on down in the Bay Area. You could spend a lot of time partitioning and taxonomizing the interop problem, but I’d rather think of it from the business point of view.
The question that seems more important than all the rest is “Can I afford to switch vendors?” Let’s consider some examples.
When printers wear out, you can buy new printers from whoever with little concern for switching cost.
If you’re unhappy with your current servers, you can replace them with models from lots of vendors (Sun, Dell, HP, IBM, others) without worrying too much about compatibility (well, you may have some racking and cabling pain); the issues are price, performance, and support.
If you’re grouchy about your OS, you can move between *n*x flavors like Debian, SUSE, and Solaris pretty freely in most (granted, not all) cases; with maybe some deployment and sysadmin pain.
If you’re unhappy with your desktop environment, well too bad, you’re stuck. Your users are too deeply bought into some combination of Outlook calendaring and Excel macros and Sharepoint collab. The price of rebuilding the whole environment is simply too high for most businesses to consider.
If you’re unhappy with your Oracle licensing charges, you probably have to suck it up and deal with it. SQL is a good technology but a lousy standard, offering near-zero interoperability; the cost of re-tooling your apps so they’ll run on someone else’s database is probably unthinkable. Like they say, you date your systems vendor but you marry Larry Ellison.
It’s like this: CIOs looking at technologies don’t want to marry their cloud service provider. That’s all.