The death of my router -- very strange episode.

We use a Netopia 2247 wireless router which serves 4 desktops via ethernet cables and up to 5 laptops/netbooks by wireless connections.
About two weeks ago two of the desktop users started complaining about low internet speeds. And indeed using the Speakeasy.net speed test showed that, in general, the d/l speeds these two guys were getting were typically between 5-15% of what we were getting on 5 other computers that we tested. U/l speeds were unaffected.
All of these 5 gave both d/l and u/l speeds which were absolutely normal.
Now, the two computers with the problems did have rather long ethernet cables (20-30 meters) but they had worked perfectly as such for at least one year on this router.
Anyway, we brought a new HP Mini netbook to one of the troubled computers, plugged in the ethernet cable and disconnected the wireless connection. Now the speed showed normal d/l and u/l speeds.
So, we did a complete virus scan and a complete Dell hardware diagnostic test. Neither showed any problems.
We also re-installed the ethernet card driver but no improvement resulted.
On the following day, the router started to lose the internet connection (internet light turning red) so I called the ISP (Eircom) who said they could see something was wrong. So they did "something", which wasn't explained to me and everything seemed to work fine for the next 24 hours.
Nevertheless, the two desktops with the internet problems continued to have them but none of the others did.
Next day, the internet light turned permanently red.
Called the ISP again and after a few tests, it was concluded that the router had indeed passed away. However, this was Christmas Eve and there was no chance I would get a replacement router before December 30. What, Christmas without internet? Unthinkable.
Then I remembered that the router that failed was actually itself a replacement for a Netopia 3347nwg router that had been showing signs of distress about two years ago. So the ISP had sent me the 2247 as a replacement asking me to return the 3347.
Luckily, I never actually returned it (mostly through laziness).
So I hauled it out and it worked perfectly on ethernet connections.
Then I got wireless working with WPA-PSK encryption and again this was perfect.
However, the biggest surprise was that the two computers showing slow internet fully regained the old speeds. I was amazed and indeed relieved as we had decided to reinstall Windows on both of these computers but had quite gotten around to it.
I still don't understand why a dying router can provide perfect internet speeds to a majority of computers but persistently serve vastly reduced d/l speeds to just two of them. But that's what happened.