It's not necessarily unreasonable, it just depends on what kind of product they want to offer. S3, Google Storage, etc. do not have a maintenance window that I'm aware of. That's not to say they would never go down, but if they do you would expect an alert and an apology, at least. Many application require this kind of expected uptime, but of course there are others (backup, etc) that would not.

Yes the request would turn into - please remove the maintenance window, instead of "make the maintenance window not have downtime"