I think you are missing a large number of users (Grandmas say) who don't customize their computers and only do the minimum : They do only what the computer tells them to do.
So these users will see the plug-in prompt Google Wave when accessing Google and would be likely to act.
Doing so will ensure that even Grandma's browser has modern HTML5 features. This will make web developers happier.

Google is working on these plugins to ensure their platform has the broadest install-base and give them a way to influence current or future compatibility issues.

This is a pretty smart move for them to maintain and grow their reach. Also - as long as they keep their plug-ins open - a positive move for whole web-app, software as a service 'movement'. (I'm not sure if it's considered a 'movement').

Don't forget Tannenbaum: "Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.Computer Networks, 4th Ed. p. 91"
And sneakernets in general: http://en.wikipedia.org/wiki/Sneakernet

I agree with with what you are saying. Especially from a technophile point of view, the app store and ovi store are not equivalent in that the ovi store is not the only way to install apps.
The C64 emulator might not be able to be added to the ovi store (if they consider it a threat to ovi); also an app manager might not be added to the ovi store (if they consider it a threat to ovi). But if you know how, you should still be able to install those things on your own.

The C64 emulator was removed from the AppStore => With the N900, the equivalent service will be the Ovi Store.

The OVI developer terms of service state (from Terms and Service link at https://publish.ovi.com/login): 5.4. Non-Compete. You may not use the Program to distribute or make available any Content whose primary purpose is to facilitate the distribution of Content outside of the Program.

So Nokia might not allow this app on their store either.

Application Signing is how Nokia is going to control how people distribute applications for this device - this control is a big deal and is not explained in the article. It is a big deal because it determines how "open" the system is: If Nokia has to approve all applications then is this system open at all?

The link to Symbian's Open Signed Online is an S60 version of how Nokia has done "open" before. I don't think this is the kind of open that people are hoping for, but unless we hear otherwise, it's the type of open we should expect from Nokia.

Another way to consider the benefits of this phone is to ask how many people have really ever used Symbian's Open Signed Online? Are you. then, the only ones that are supposed to be excited about this phone?