Thanks again, burnout, for a very informative reply. I didn't know OM was dead, but I guess I'm not surprised. I'm on slimjet, another blink browser, and now I see there is a class of opera extensions that will not install on anything else. I currently have an feed subscription extension, but all its options are for online readers, with the exception of "default reader", which is why I wanted to register OM with Win7.
Maybe the answer is to use a browser-based feed reader. What's keeping me from dropping OM is that Google uses redirection to count clicks even internal to our emails, and I think that is over the line. Slimjet has a setting to stop that on google searches, but I don't think it applies to gmail.
The workaround does exist, but it's to manually copy and paste the feed url into OM, which isn't too onerous at the moment.