I certainly understand and agree from the perspective of what we would like. I would like a system that allows me to trust the keys of people I trust (like one mjg59) and secure my systems to only boot things he signs -- but from a practical matter:
Yes, I think it is reasonable that Canonical would want to allow its distributors to make a product based on open source software that is in fact more restricted than what one would get by purchasing an MSFT product.
If a distributor told Canonical "we will use Ubuntu only if we get to completely lock it down," I would understand that Canonical would say we discourage that, but won't stop you. I don't like those kinds of products, and I wouldn't buy such a product, and would discourage others from buying it, but I don't think Canonical should say no and don't think worse of them for saying yes. Their bug #1 is that Linux is not the most used operating system on the desktop, anything to get desktop linux (ie gnome/kde instead of android) into the hands of end users is in the interest of closing their bug #1.
In many ways this is just the Android debate all over again, but on the desktop. I'm not thrilled with Android, but I don't think its been bad for software freedom in general, as its a heck of a lot better than the iOS everything road we were down. Maybe I'll eat those words in 10 years, but at the moment that is how I feel.