This is a per-server setting... like i said, you can negociate to have your site on a different server, under different configurations... you have to pay for what you need... (i actually have my own hostgator account having the mailing limit (200 emails per hour) raised because i have negociated with them that i needed to send email all day long...)

and you are right, there is no security risk with bigger files... just a larger risk to have people uploading porn or pirated softwares... and this is against their policies... i suppose this is a way to avoid a part of it.

anyway, when are you in need to upload a 50 gigs file?!