1) "Android apps are written in Java" I haven't delved into the deeper end of things, but I suspect that it will be a matter of time before people start putting other compilers on there. I mean, Jython and JRuby are implementations of Python and Ruby for use on a JVM. So given that the phone is as open as it claims to be, it should eventually happen. I know the Haxe people are talking about porting Haxe onto android. I'm going to guess it's just a starting point to use Java.
As for the middle layers being closed, I don't see it mentioned explicitly in the design overview, and a browser is in the app layer, not the framework layer so you can replace that for sure.
2) "the installable application is dead" To think that a mobile platform is simply a smaller web that you can take with you is a bit misguided, I think. As an example, currently, no web browser provides GPS data from the user. There's a plugin for firefox, but that's about it. So (as an example) until mobile browsers provide geo-location, you'll be limiting yourself to writing applications that confer the advantages of the web, but not of the advantages of a mobile device.
Native applications will still have their place. Just as TV didn't replace the radio completely, web apps won't completely replace native apps.
His other points seem to be better justified, but at this point, no one knows. Only time will tell.