I feel your pain...

Unfortunately I think you are the victim of a confusing design of their site that also tricked me. I did exactly what you did last week and came to the same conclusion, but then I saw a different page that listed the cards compatible with the 8300 series and it did not list the 6GB card. I was confused by the discrepancy at the time. But, here is what I finally realized is happening:

Given the sequence you went in, the page in step (5) would appear to be saying "the product on the page you came from is compatible with the following phones", but that isn't what it is saying. The device fields in step (4) have the caption "Find a SanDisk product that is compatible with your device:". In step 4 you only narrow down the device type and manufacturer. When you got to step (5) you were presented with 3 phone models and those model names are clickable links. You then need to click on one of the links and you will be taken to the page that lists which cards are compatible with that device.

Unfortunately, following the sequence you used, one is easily led to believe that you've ended up at a page listing the devices that are compatible with the product you came from. But, going from step (3) to step (4) you actually lose association with the product and end up in a generic compatibility guide.

I notice that today the links don't work in the way that your script suggests that they do in so far as after clicking (2) the option to click (3) no longer exists - instead you end up at (4) directly. You can enter the values you indicate in that step and end up at (5). At that point, since you never went through the page in step (3), there is no tendency to believe that you are looking at a device compatibility list for the 6GB card - the visitor is now, never having seen any product pages so far, more likely to click on the "8300" link and find the list of compatible cards and see that the 6GB is not listed.

Does that help clarify things?