I think the main reason for this line of thinking is that people will jump sooner at a title with a lower pricetag. Also if that was the originally intended pricetag, they will expect less quality. As anecdotal evidence of this, a friend recently linked me a video of Black Light: Tango Down. Before I could watch it, he was telling me, "yea it looks sort of shitty, but it's a $15 game. We should try it out!" He later told me when I showed him some Crysis 2 footage that it looked just as shitty as BL:TD and wasn't interested. So he'll buy a shitty game if it's only $15?
I know I've fell victim to the low price point before though. I buy games on Steam that I already have or wouldn't have bought without a sale, and I buy games on XBLA just because I might want to play them at some point and they're cheap.
The problem with F2P though is that too many companies get it wrong. The purchasable content needs to be something you're tempted into buying, not forced into buying. No fucking tiny backpacks with a bigger one to buy, or consumables to keep from being underpowered only being available in the online store. Look at WoW's celestial steed. That shit is cosmetic only, and it sold in obscene numbers. If you want to do bags, look at WoW again. People can craft up to 20 slot bags, or 22 if they make the expensive ones. You can buy a 24 slotter off a vendor for like 5000g. Put that shit on an online store. Most people deal with 22 slotters, but those with money to burn with want the bigger one. People have to farm heroics for badges to buy gear. Let people buy badges with real money. They'll get their shit faster and easier than the person who farms it, but they're not getting stuff that non-payers can't get.