In a closed environment Apple will win because the iPhone just rocks from the point of view of the quality and design of the UI, the amount of applications, and so forth, but something really open can contrast the iPhone using the Apple everything-close policy against itself.
Also, openness is not necessarily a good thing - specially for mass markets. If people really, really wanted to 'replace the whole operating system', wouldn't they all have migrated to linux (on its thousand formats) already...?
It's not the telecom's responsibility to support your phone's OS any more than it is your internet provider's responsibility to support your computer's OS. The point that was made is that an open device, analogous to the PC in the early computer days would be a Good Thing for the phone ecosystem.
That said an open market where the user can upgrade to the next version of Android, or to a custom version of android, and generally, when the vendor of the OS is not necessarily the same as the hardware vendor is a good thing.
But the question is how much willing the operators are to let the user customize their handset. Operators are definitely not going to like android's statement of openness to users.