That's of course a generalized "presumption".
I haven't seen any consumer survey or report that proves using statistical data, that people actually bother to check the WHOIS info before making credit card purchases.... Let alone having any clue what a WHOIS info is, and how to check for it.
Every web server I ever bought over the last 10+ years I have. Think more tech minded people will check things like domain registrars, hosting, ppc ad networks, etc... I know I spend 5-10k minimum online each year between domains, hosting and advertising and none of that goes to anyone with anonymous whois and I'm just 1 guy so no matter how small the percentage gotta think it hurts sales as I have personally aborted purchases after finding that, unless your info is posted on your site but most anonymous whois sites I have encountered don't list any address/phone on the site as well and an email isn't good enough for me.
In 2012 consumers are smarter and quite a few are looking for address, phone, email, reviews, BBB etc... before the plastic comes out. More information posted on the site better trust established.
I have added phone numbers to sites with no other changes made and seen substantial increases in conversions.
So yes a "generalized presumption" based on myself actually backing out of shopping carts after reviewing who I'm buying from and finding private whois as I see no reason for a business to do that. I could see if your photographing celebrities and want your location hidden but most businesses should have no reason to hide that unless running illegal pharmacy, adult or working from your mom's basement and pretending to be a big dog. :D
Years ago I had bought a domain and it came with free privacy. Forgot about it and when a guy finally got a hold of me after paying a registrar to contact me said he was trying to find me for months. End result was hand regged name sold for $7500 so as far as domain sales go definitely good to make it easier for buyers to contact you.
Better off with a PO Box for a few bucks a month and your own email address created just for your domains whois sent direct to you then an email like domainprivacyservice587654@ which may show up or might not since thousands of domains use the same email address or a variation of it.