I think that this limit is an outcome of a limitation the product has with the live monitoring sessions.
With the live monitoring session, sampling too many ports at the same time consumes to many resources and can also pose heavier load on the fabric (every counter polling introduces traffic) - this is why the guys limited the amount of ports you can sample at the same time.
with the history feature, the behavior is the same but i am not sure about the amount of load. i can have somebody look into this.