I can't agree to that. Naturally you'd think vintage LED watch prices should raise over the years since there should be less of them around every year. Ironically it seems there are more of them available than like 10 years ago. In 2014 you can get a working vintage LED watch as a "Buy it now" for 45 USD, even less in auctions. And 45 USD are worth less in 2014 than they had been in 2004.
It's hard to pin that all down to one brand - in 2005 there were more National Semiconductor or Commodore around since someone discovered a box with 500 NOS watches back then. In 2012 someone discovered a box of 500 NOS Compuchron, so this year obviously the compuchron are cheaper. Also Synchronar seem to be more common recently. I think it's impossible to find a time when there are not at least 3 for sale on ebay these days while in 2005 you'd be lucky if more than 1 popped up a month.
I don't take statistics, but from my guts it feels like generally prices rather went down. Maybe not specifically for Commodore or NS but generally i mean.