There is no "have to" about this. Nowhere does the original article say Silverlight will be used *exclusively*, but the post on Slashdot says as much. Yellow journalism, anyone?
Hulu has been advertising that they're showing the inauguration for several days now, with a countdown to the start time and everything. And Hulu works just fine on my Ubuntu machines, the fast ones at least..
The Linux community seems to be very invested in being perpetually misunderstood and discriminated against. Get over yourself, guys, and get the facts before whining about something that's not even true.
I feel like I should speak to this as extensively as I can, since I'm self-employed as a tech support guy, and around 95 percent of my 250+ clients are seniors.
The suggestion about using Ubuntu is a good one, but Ubuntu may not be going far enough in the direction of ease-of-use. I'm surprised more people don't seem to be aware of Linux Mint, which removes the hassle of installing video codecs and browser plugins, so the setup process for a basic user is two steps - 1. Install the OS, and 2. Install Acrobat Reader and the browser plugin for it. This takes around half an hour, and then you're done, and Mint 6 is based on Ubuntu Intrepid anyway, but the menu is a bit slicker (imho), and the artwork more polished.
Putting icons on the desktop for the browser and the email program, and also the word processor, is essential, of course. Ubuntu or Mint is a great Windows replacement for nearly any beginning or advanced user - it's normally only intermediate users who want to install lots of random crap from the internet who might get upset when they can't under Wine. In my experience, most seniors fall into the "basic user" category anyway, so they won't really notice a difference between Windows and Ubuntu unless they're already dependent on AOL 9.
With seniors, the most important thing is to be not just patient but reassuring. Many seniors have a mental block against technology, but if you patiently reassure them that yes, they really can figure it out if they just read everything on the screen and use logic, eventually they'll believe you and try. This can be time consuming at first, but in the long run it will save you a great deal of time as they start to become self-sufficient. It's a natural human tendency in most people to bug someone else if you think you can get away with it, rather than trying to fix your problems yourself - training that out of a person can be tricky, but is ultimately very beneficial for both you and your time.
According to the latest official figures, 43% of all statistics are totally worthless.