I wonder why we have a limit in the spam flags. Should we not have a limit to flag spam post? I am curious to know why we have that limit. :).
The limit is a system wide thing; all of the SE sites have the same behaviors, apart from a few minor differences.
There is a limit because the spam/offensive flag gets misapplied and abused on some of the other sites. As your flag weight increases, you get the opportunity to flag more things per day.