No SD kills it for me. $50 for only 8gb more when a 32gb card is $30 is Apple-like and kills it for me (not to mention that the MTP method of getting files onto/off of ICS is way too slow, whereas popping the card out to copy large blocks of files is nicely fast.)
You're comparing two different kinds of memory. Nand memory used internally are vastly faster than those used on SD cards and therefore more expensive, even more so after Apple having more or less cornered the market on these chips.
The slowness of the MTP protocol has nothing to do with the speed of the underlying flash, or it would be equally slow to put it in a card reader (or with a ROM that supports it, mass storage mode.)
Second, while for a limited subset of apps, even a high-speed SD card may not be fast enough, for the kind of bulk data storage I do and I'd guess most people do with their phone, the difference is a triviality (and even some SD-to-app movement on my phone, although the way storage is structured on the GT2 and most ICS phones eliminates that ...since the "SD card" is internal and the actual/external SD card is a 3rd tier of storage.)
Lastly, SD cards
are NAND flash (the alternative, NOR, are tiny and slow to write to); they're a cheap grade of MLC, although how cheap will depend on the speed rating of the card. Much faster MLC is available (for example what's used in SSDs, both in slower async and faster sync designs) and SLC which is MUCH faster and longer-lived but much pricier.
I'm not sure what you're saying is used specifically in tablets and having looked very little into the internal design of them, I'll have to take your word that there's something specific used in them that Apple is buying a lot of... but I'm not sure what the supposed benefit is supposed to be and given that other sorts of flash have prices that have just about crashed in the past six months, well, that would only be more reason to let people add in a card with the cheap stuff.
*shrug* I don't begrudge Google making a bit more profit on the 16gb model, but the real cost of flash is down around $1/GB
retail.
eta: Since people have done teardowns on the Nexus 7 already, one can see what kind of flash it uses -- a Kingston eMMC module (Samsung uses their own eMMC) - which in essence implements the predecessor of the SD card protocol, and should perform similarly to a very high end SD card. For that matter, you can buy single units of the flash they buy use
for $17.90, and chips like that are usually
very heavily marked up for single units...