Honestly, what was Sony thinking regarding Vita memory cards?

[Super_Boom]

I assumed it that system was being sold a loss (or a very small profit) at launch, and selling proprietary cards was a way to make up that expense.

Piracy was also an issue I'm sure...but like you said, it seems it hasn't been a problem for the 3DS yet, so I'm inclined to think the expense is a big part of it.

It is a pain though...especially with how handheld devices are ideal for digital games.