Q: App Store: says You cannot update this software since you have not owned the major version of this software - when it came with the computer!!

Bought Apple iMac about 3-4 months ago and ever since I have had it I have not been able to update the Apple applications, i.e. pages, iphoto, keywords, numbers etc etc

When I go to the app store to update them it says "To update this application, sign in to the account you used to purchase it." which I do several times and then it says

"You cannot update this software since you have not owned the major version of this software"

What the ****! It came with the computer so have never needed/had the major version, how do I get them to update without removing the receipt file and downloading it manually every time?