This is true and is probably the reason you don't see as many of the all-silver coins in the marketplace. The initial investment to obtain these is terms on BTC was much higher due to the premium conversion at the time. There were more of those minted than the Gold B version (1300 vs 700), but the initial cost was probably in the 2BTC+ range.
Which coin is more valuable?
Which have been selling for more?
I haven't noticed a difference in the selling price although when BTC was cookin' in December, the Gold B silver coins were selling on eBay for $3k regularly.
I agree with Luke on the current pricing as the latest offerings for both versions have been in the 2.35BTC range and I am currently selling one for that price.