Lots of questions and tips on this for Exchange 2007 and 2010, but I can't find anyone having these issues on Exchange 2013.
In short, I got hundreds of users, none of which are currently receiving the mailbox storage size limit warnings, not for their main limit or for their send limit. I dont use receive limits.
Doesn't matter if its an individual limit or if its a DB limit, no emails are sent notifying the user.
My warning message intervals is just the 2013 DB default of 15 min at midnight.
I'm on Exchange 2013 SP1/15.00.0847.032.