I agree that the Shaw business package is over-priced compared to the residential equivalent. That being said, for a business the cost is relatively small in the grand scheme of things. The business package also comes with static IPs and a somewhat better level of support than residential.
As for local hosting, of the six things you list, "control, speed, storage, availability, bandwidth, cost" I would agree with you on only one, "control".
For organizations that have a philosophical or legal requirement to maintain complete ownership over their systems, then they have no choice to host their own mail.
But for most of the other things you list, the advantage is with the cloud. For example, availability. I'll put Google's up time against any single local hosted server any day.
And cost is significantly in the cloud's favor. Whether or not you already own the server, you still have to pay to maintain, backup, provide power, cooling, and pay someone. And in most cases license software as well. For a smaller business those costs calculated on a per/user basis are enormous.
And getting back to availability, what happens when it dies? By the time you source new hardware, rebuild and recover you are looking at a significant outage.
As for storage, most corporate mail servers do not have 7 Gigs of storage per user and that is what you get for free just as a starting point with Google hosted corporate mail.
The switch is completely transparent to the end user. They can continue to use the same email client they always have but as a bonus they can now use an excellent web-based client as well for checking email remotely when they don't have their laptop with them.
Again, for large corporations it maybe(?) still makes sense to host locally but for everyone else it's overwhelmingly in favour of the cloud. I'm not saying there aren't situations where self-hosting makes sense but those are increasingly rare.
By the way, I didn't understand your point on spam. Google's spam filtering is near perfect. Much better than any of the commercial spam filtering products I've seen which makes sense since Google can aggregate spam reports from thousands of users to "learn" spam.