I think it's inaccurate to say "Android" isn't "truly open". It's open when it leaves Google and the code is still out there. I can still benefit from that openness even on a phone that carriers added some restrictions to.
The blame should rest entirely with the carriers.
This isn't "Apple vs Android" this is "Apple vs Carriers".
The fact that there are multiple suppliers give the user choice. They can include how locked down a phone is in their criteria for making that choice, and buy one direct if they wish to have a phone that's not locked down by a middleman.
(Not that people won't figure out ways around them, but if Android were truly open to users you wouldn't need exploits to get around limitations...)