Or it will be a way for SNK/Playmore to get SDcards into the hands of buyers so they will have room for buying more roms. I highly doubt they plan on selling all the extra games like this.
A 20MB game on a 4GB SDCard is a little silly. They'd also have to sell them for $20 or so and that would be too much for a rom.
You're probably right about some of the games just being for download, the X has 2 gigs internal memory already, but I still remember when they made 256meg and 512meg SD cards, there's no reason to assume that these are 4gig cards. Also if this render is accurate, then that square missing from the side of the cart is where the copy protection switch is, meaning this card is stuck in read only mode and you cannot put content onto it. Just like you had to cover that hole in the bottom of a store bought VHS cassette with tape if you wanted to record over it.
I'm actually wondering if you'll be able to save ninja masters to the internal memory from the card, if a lot of these games do come out on cards I'm not gonna wanna carry them all that's for sure. Of course, as has been pointed out, it's Linux based so it won't be long after launch we'll be able to do anything we want with it lol.