Unless you're buying a cheap accessory the benefit of purchase protection with a credit card (or prepaid card) far outweighs any perceived advantage of a cash purchase. I think that advantage alone would discourage cash sales.
Credit card sales only work if you not only have a credit card but also if the CC people will allow your purchase. I've tried calling the CC people the day before I wanted to buy a MBP, went through all the security questions and identified myself, told them where I was going (The Apple store in xx location), how much I was going to spend ($1800), etc and they said "OK, I will mark it, but the system may still reject your purchase." Went to Apple store the next day and Surprise! Even though I called and had more than $ 6,000 of available credit and never carried a balance they still declined the purchases (and of course blocked my card as well). I knew what was coming so I paid cash and the store people had no problem accepting $1800 in $100 bills although they did need a manager to check the bills. When I got home I called the CC people and said "Why did you decline the purchase? They told me it was because the system flagged it as unusual and probably fraudulent or a stolen card and the system could see no reason to allow it and also because I had not called in advance to let them know! Then after I identified myself again and went through all those hoops again, they said "OK, we'll remove the block and you can use your CC again so you can go back and buy the computer." I told them "haha I knew you would reject it so I was prepared and paid cash." they said "Why pay cash? You could charge it!" Dumb cc people. Never figured out why they keep doing this to me. They don't seem to keep records long enough for me to make my bi-annual Mac purchase legit. Maybe they hate people who don't carry several thousand dollars in balances every month?
Every time I make a purchase more than $100 in an Apple store I have cash just in case. It seems that Apple stores are huge targets for stolen credit cards since the products can easily be resold for a good amount.