g1smd - 10:47 pm on Jun 11, 2010 (gmt 0)
Yes, it's quite logical for "Acme Widget Mk I" to be redirected to "Acme Widget Mk 2" when the former product is no longer available.
It's also not a problem for both "Acme Widget Mk I" and "Acme Widget Mk II" to be redirected to the "Acme Widget Mk III" page.
If both of the old products each had a "specs", "accessories" and "review" page, you might have simply decided to telescope all of those to the main page for the new product... however, you appear to be better off redirecting both "specs" pages for the old products to the "specs" page of the new product, both "accessories" pages for the old products to the "accessories" page for the new product, and both "reviews" pages for the old products to the "reviews" page for the new product.
Taking it further, it's certainly not seen as legitimate for 100 "Acme Widget" pages and 100 "Acme Gadget" pages and 100 "Acme Doodad" pages to all be redirected to a single target URL. That would potentially be seen as trying to manipulate PageRank.
After following just "one" of the redirects, the searchengine would have already found the new URL. Spidering all the other redirected URLs, and with all of them having the same single destination, would be seen to be wasting the crawl budget of the searchengine.