I just got off the phone with Walmart.com customer service. I had no problem getting the 10% credit on the two notebooks I bought. The rep said that the 5GB description was a misprint, and she apologized for the error.
My impression was that I would not have been offered the credit had I not called. So, it can't hurt to try.
This is a slightly abbreviated summary of the conversation:
Rep:
<< Walmart.com, how may I help you? >>
Me:
<< Hi, I bought a couple of HP notebook computers at Walmart.com a few days ago. They were advertised as having 5GB hard drives, but when I ran the HP diagnostics, it showed only 4.3GB. A friend of mine also bought one, and when he called yesterday, he was offered a $75 credit to his account. Am I also eligible for the credit? >>
Rep:
<< Let me pull up your information. You are Mr. Xxxxxxx? (note: they apparently have an Automated Number Identification, ANI, so they knew immediately who I was). What is your order number please? >>
Me:
<< My order number is xxxxxxxxxxxxx xxxxxxx >>
Rep:
<< Yes, we are offering the 10% credit. The description on our website was not correct. We do apologize for any inconvenience. >>
Me:
<< That's quite alright. Thank you very much! Will the credit appear on my credit card? >>
Rep:
<< Yes it will. Thank you for calling walmart.com. Is there anything else we can help you with? >>
Me:
<< No, thank you, but thanks very much for your help.... >>