I suspect the fact that this game has animated cutscenes that is has something to do with only one file to save. You know, cutting off save files to add more content. (And if it's not like this, sorry. I thought save files took up a good amount of memory).
I'm pretty sure the portion the game saves would take is independent of the main memory, and more importantly would be trivial in comparison to what a movie would take. In fact, IIRC they cap out at 512 kilobytes, and that's more than enough for what this game's memory demands seem to be, extremely excessive if anything.
Normally I too am not a fan of only one savefile (I often like to keep multiple save files in my RPGs), but it actually didn't bother me in Solatorobo. This was a game where I didn't feel I needed multiples. Maybe because it was skewed easy, I dunno.
Just for myself... no, it's not a big deal, because I doubt Solatorobo's anywhere near as buggy as something like a Bethesda game where I'd be making multiple saves like crazy are a precautionary measure to bugs, such as the one in Oblivion that rendered newer saves unusuable, nor does it seem like a game where there's really alternative approaches I'd want to use. At worst I'm simply unable to do things like start a new game to see how it started again after I beat it, and it probably comes with a NG+ thing anyway to negate that point. My main beef is how it inhibits sharing without a solid justification, and that probably IS the intent of it. I question how much that really matters, you might get a few more sales but I figure quite a few people, especially in families, would either see it being as pointless to buy copies for EACH person as buying everyone their own copy of a movie, or just delete the save when another wanted to play and thus only serve to frustrate people (if they're fazed at all) without generating more sales.