JNewell,
With your bargain 1200 you've got a gun that's been out of production for almost 30-years and made by a company that's changed hands a few times since then. It's virtually an orphaned gun. For the 870 buyers, Remington continues to make and support 870s.
IIRC, in 1964, the Model 1200 was Winchester's replacement for the discontinued Model 12. There's nothing wrong with the 1200 (and it's 1983 successor the 1300), and some feel the 1200's fast cycling is worth the additional cost. Its ills were market related and had started a decade earlier -- the new Winchester pump was too little, too late.
The Remington 870 Wingmaster had been eating away at the Model 12's market share since its introduction in 1950. The Model 12 was a higher quality pump gun than the Wingmaster; but, most folks weren't willing to pay extra for the M-12 because the Wingmaster was a great performer. Discriminating shooters were willing to pay more for the M-12, but their ranks faded. In an exercise of unfortunate timing, just as Winchester introduced their down graded 1200 pump, Remington blew them away with the all new Model 1100 gas operated auto-loader. IMHO, if it hadn't been for military sales of 1200s during the Vietnam war ear, it may not have lasted as long as it did.