I have some feedback on your points as well:

MAC users have done it for how long?
In fact, Mac does have right click and context menu feature since Panther if I’m not mistaken. It’s just not turned on by default, but now Apple is even inventing on new way to display context menu. So the trend of right click, I’m afraid, is simply undeniable.

How do you assign specific keystrokes or shortcuts to concepts that a designer has just come up with?
RIA, I think, is mimicking the way Desktop application is built so that end users can have the same expections for RIA as they are using Desktop application. If you are in Word, you can press Alt+F to display the File menu. If you are at data entry screen, you can press the character in underline to go to that field automatically.

It’s unfortunate, given the state of Beta 2, Silverlight doesn’t have a built-in way for that yet. Sure you can handle the OnKeyDown event handler, but that will be way too much coding. Probably they will make it as built-in feature in the final release, let’s just hope

Regards,
Jimmy.

I did want to respond to your overall list of RIA challenges, however. .. I will speak both in general, and also specifically referring to Flash/Flex, because that’s where I have a better understanding..

1. Good-bye to “Back” and “Forward” button.
This is true. However, this is true even for AJAX. We have to remember that the “A” in RIA stands for “application”. Once you’re within the application, you’re within that experience. Back and forward can be used to advance within the actvities within the experience, just like undo and redo in a typical desktop app.
For some people this is disorienting, but this is only because we’ve allowed RIA to ‘sneak up on us’ without really appreciating what is it. I heartily believe that this is the desired user experience in the long run, and people just need to learn this capability exists.
I will add, though, that history management is possible with the Adobe suite of RIAs, I believe Flex 3 may do it natively? There are ways to modify the URL while engaged within the RIA so that the back and forward buttons do in fact shoot you out of the experience. I believe silverlight has the ability to interact with the page outside itself, right? So it could probably be managed as well.

Can’t live without context menu (right click).
MAC users have done it for how long?

No copy-paste.
Again, this must be a limitation in Silverlight. You can certainly copy and paste from .swfs, if the text elements are saved appropriately. I’m not sure about “select all”, however. This is actually probably browser specific, since for .swfs at least, the means by which the plugin is embedded is different (object vs embed). A user cannot “tab” into a flash movie in Firefox 2 (not sure about 3, but I suspect not). Therefore I would expect that a select all would not really allow them to capture what is within the RIA itself.

No hyperlink.
Whaaa? I find it hard to believe silverlight doesn’t support hyperlinks? Although once again, these are applications. Would you expect excel to randomly have hyperlinks in it? No, an application is intended to allow a user to perform a specific task.

Very minimal keyboard support.
It’s interesting that Silverlight doesn’t have strong accessibility support, since Flash and Flex leverage the Microsoft Active Accessibility API to do their accessibility

In general it’s tough to contrast the controls within a rich experience like flash or silverlight with HTML. HTML has a limited set of tags to markup content. Flash and Silverlight are less about “content”. How do you assign specific keystrokes or shortcuts to concepts that a designer has just come up with? This is why it’s important to have a library of components to use and reuse. The appropriate keystrokes may be learned by the user to perform certain tasks. I would be surprised if keystrokes couldn’t be assigned in Silverlight, but the challenge would be in educating users in how to use them (the same problem that traditional web applications suffer with access keys)

I think it’s great that you’re looking at this stuff from the users’ perspective! Often I think we technophiles get so excited about ‘the next big thing’ that we forget to consider the overall usability!