According to The Knot's weddingchannel.com website, "a groom's cake originated from the South, and although it used to be viewed as an added and unnecessary expense, this once-neglected cake has been making a huge comeback. Intended to be a gift from the bride to the groom, the groom's cake is usually dark (often chocolate or liquor-soaked) and designed with a nod toward what's traditionally considered "masculine" (i.e., no rosettes in sight)."
The latest trend is brides creating a groom's cake to reflect his interest or hobby. The groom's cake can be presented to him at the engagement dinner and/or party, rehearsal dinner or as an alternative choice to the bride's cake at the wedding reception. "It's customary for the groom's cake to be displayed next to the bride's cake and later cut and put into boxes for guests to take home. And believe it or not, legend has it that single women are supposed to sleep with a slice under their pillow the same night they receive it -- and if they do, they'll dream of their future husband." --weddingchannel.com
So to answer the question I posed, is it necessary to provide a groom's cake at your wedding - the answer is no. This is something that is totally optional and something that you should want to do, not something you feel obligated to do...though I think it adds a nice touch to your special day and will make your groom feel a little special.
Ciao for now,