it's only in the last couple of years that we have actually gotten there, through wider 3G/4G coverage
Which carries a substantial recurring fee. I already pay for Internet at home. Why should I have to pay again to be able to use my own computer while riding the city bus?
If course, you're not paying to use your own computer, you're paying for Internet access while you're on the go. You can use a Chromebook while offline now, you know.
I may be a bit privileged in this area, as we have free wifi on the busses and trains around here. And my mobile subscription is $17/month, which includes 3GB data. That's actually quite a lot of data, even with heavy use of my phone for tethering and watching Youtube etc., the highest I've ever used in a month is 1.5GB.
Why do you think centralizing computing power is such a bad thing?
Because as implemented, it restricts me from choosing with whom to centralize computing power.
No, it's actually pretty easy to choose where to centralize computing power. Just off the top of my head, you can choose between Google (ChromeOS, Google Drive, Google Docs etc.), Microsoft (Skydrive, Office365, Outlook.com etc.) and Apple (iCloud, iTunes etc.).
Can you install an alternative browser on ChromeOS? No, because the browser is actually the shell. But you can easily use competing web-based services, no problem. So it's pretty much the same situation as with iOS, where you can only install different UIs for the default Safari browser, but nothing's stopping you from installing Google Drive or Dropbox etc. and using them instead of iCloud storage.
And why would Google want to offer alternative data vendors on their platform?
Because a country's competition regulator may decide that Google has market power over operating systems that ship on laptop computers with 10" displays and thus require them to do so.
They already offer access to alternative data vendors, nothing's preventing you from using Outlook.com instead of Gmail and Skydrive instead of Google Drive.
As long as Apple aren't forced to open up the iPhone/iPad platforms, I don't think Google will be forced to open up the ChromeOS platform.