The save limit is likely due to the fact that the game uses cloud saves. They likely limit the total save number to reduce the amount of cloud storage needed for everyones saves and for bandwidth reasons when uploading/downloading saves.
The annoying thing I have noticed is that this game creates a ridiculous amount of auto saves.. but only when you can save yourself.
If you're in a mission where autosaves are your only option.. they never save. If you have the ability to save yourself, you'll get an autosave every 30 seconds.
I really love ME:A but the save system drives me nuts. Between the horrible inconsistency in autosaves and the ridiculous idea to not allow saving in story missions, I really wonder what they were thinking when they designed this system.
Personally.. I keep 3 manual saves per character. Before I exit the game, I go to the 'Load Save' screen and delete all but the newest autosave and then I exit. I just do this to keep things clean, and because I don't need 10 autosaves that are all 25 seconds apart.