It's silly to act as if it was a Sony strategy when it's very obviously a concession made to retailers who got burned on PSP.
We don't know what retailers' margins on Vita memory cards are, though. Furthermore, DS was affected by piracy far more easily. Nintendo couldn't even update the OS, and flash cards become an easy way for the masses to play games for free. Yet retailers continued to stock a huge amount of preowned and new DS titles. Nintendo's pledge to retailers and publishers was to invest a lot in making sure the 3DS had good security, which they largely succeeded in implementing while also offering standardised external media.
I've also save hundreds, if not thousands of dollars on games thanks to PS Plus and PSN sales.
This has nothing to do with the fact that memory cards are expensive -- you'd have saved that much anyway if there was a better storage system available on the platform. Though I'd argue your definition of saving money isn't exactly a fair one - PS Plus grants you a license to play a game as long as your subscription lasts, which isn't the same as owning the game.
Nintendo's software prices are in no way comparable to that value
Nintendo's software is an entirely different matter to PS Vita memory cards, and you could spin this any way you'd like. Nintendo believes in maintaining a healthy value of software rather than devaluing it, though.
and they also expect you to rebuy your Gameboy, DS or 3DS multiple times over the course of a generation.
I own three PSPs (launch PSP-1000, PSP go and PSP-3000) and two PS Vitas (Vita-1000 and Vita-2000). I skipped the 3DS XL and 2DS. Does this mean Sony expects me to buy PSPs and Vitas several times over the course of a generation? No one is forcing anyone to rebuy Game Boys or 3DSes, both platform holders are improving on a product and offering more choice to customers which is a good thing.
That feels a lot more predatory to me than an upfront investment in flash storage for a system that was not horribly flawed in numerous ways at launch.
But your entire argument is based on false equivalence and has nothing to do with Vita memory cards. As above, even if hardware refreshes somehow were equivalent to memory cards, they aren't a predatory practice.
a system that was not horribly flawed in numerous ways at launch.
I bought Ninja Gaiden: Sigma from the PS Store for my Vita-1000 at launch. Two months later, I deleted it to make room for digital Uncharted. I lost my save data because saves are tied to the game file itself. Furthermore, writeable storage wasn't mandated on all games, so you had a case where only some games (like Touch my Katamari) would save without a memory card and others wouldn't. So it's evident that at launch, some publishers expected people not to have to buy a memory card to use the system, which says a lot about their confidence in Vita memory cards in the first place.