They probably stopped making them because of increased production costs weighed against potential sales, which is the same reason Continental stopped making their Top Touring tire (best commuting/touring tire EVER). My Conti rep (I'm the buyer for a shop) told me that if Conti re-issued that tire today they'd have to charge over $90 retail each. At that price they wouldn't sell many, so it's likely not coming back.
If Michelin re-issues the Magic Green Cross Tire it will be interesting to see how much it costs now -- and how many people would pay the higher price.
Last year I was riding the original green muds @ schooley mill when on the last lap I was pushed into thorns and flatted the front tire. I rode more than 1/2 a lap on that flat michelin mud clincher and kept my place! Will I buy more? Yes! Tubular as well please!
Well, naturally. What amazes me more is with all the design technology out there, no-one's come up with a better mud-shedder than this 'per grip'. Got some lovely treads of these on FMBs and they ooze sex.