Man, I hate it when that happens! You bite on a great deal and still stumble across a better one...
To explain my above post a bit better... most PC's tend to have 4 RAM slots. Some now come with as many as 6. But in laptops and budget model desktops there are usually only 2 RAM slots. Typically both slots are filled so manufacturers list it as "not upgradeable", hence you can't add onto the existing RAM but can only replace it outright. A few will be listed as upgradeable, which would mean the 2nd slot was still available to accept an upgrade.