meangreenie you bring up a good point with your thought on the fact that M3 never really feels like the real cart. It really makes you wonder if the supercard writes directly to the removable storage every time you make a choice or physically save like in advance wars, or whether or not somehow it does it at a specific time like the M3 but the M3 just happens to always take longer.
If that is the case, maybe the reason for the delay is behind the M3's ability to have more than one save even for NDS carts. However, I don't think that is the reason.
I think the reason is because the M3 copies the save to a single SRAM slot when it loads a game. It needs a battery in order to keep this data alive for one reason or another after you turn off the DS without going through a saving process. In order to utilize this single SRAM slot for another game, it needs to copy it back from the SRAM, and then load the SRAM with another set of data for your next game. The only time the M3 can do this is if you tell it to (soft-reset), or when you turn the DS back on, because a DS turned off is without function. The M3 probably can't do this at any time the SRAM is changed, because then it would be using it's resources to so a simple copy/paste job and you'd notice it in game, such as when you fail that Warioware minigame because the M3 decided to copy the save at that time. This would also defeat the purpose of the SRAM entirely and more, screwing up your gaming in the process.
What the supercard probably does is patch the game ROM to direct it's saving to the CF card. This is great and everything when it works, but it's probably been this fact that caused me to lose my meteos savefile when I was told I needed to use the SRAM in a real DS Cart to play Tetris DS when it first came out. Also, correct me if I'm wrong, but this has been a problem in other DS games as well such as the recent Rockman ZX.
You ask why can't the M3 do what the supercard does for saving games, and I might ask why can't the supercard do what the M3 does? But I don't ask... because I know the answer: it doesn't have SRAM because the company that makes it wanted to cut costs and price for their consumers.
If the M3's SRAM works so well, why would it's creators want to hack every DS Rom to save to a different memory type? There's probably craploads of tough programming involved that probably isn't worth their time considering the only hiccup of the SRAM saving is the couple seconds of waiting you have to do every time you boot up. The entire time they'd be programming new saving method patches into their software for every DS game, they would actually be hurting their cause because they would be making their use of SRAM and rechargable batteries obsolete. They might then, after doing all that programming, decide they could cut costs by removing the battery and SRAM entirely. This might even hurt their GBA compatibility, and then maybe they'd change their name to the SuperM. Then Nintendo would file suit against them for implying the word "SuperMario" Then they would be out of a job or worse, go to prison and get the wrong side of buttsecks every night, without the common courtesy of a reacharound. Tell me, why would they want to start this chain of events?
I think the M3 can save to the memory card, but it chooses not to. The Supercard, however, can't save to it's own SRAM because it doesn't have any.
edit: I apologize for my extremely long posts