No, it really isn't. Everyone can talk. Rap is a skill: Only a few can do it, and even fewer do it well. On the technical side, the best rappers use internal rhyme patterns, complicated inflections, and double-time and triple-time rhythms that take years to master—to delivery words as vivid, lever, thoughtful and poignant as what you'll find in the Norton Anthology of American Literature.
Rap takes practice. You could literally hear MCs like Lil Wayne, Kanye or even Fat Joe get more skilled over the years, with each successive album and tour. But talent is important too, and not everyone can grasp the physicality of rapping: Guys like Diddy and Dr. Dre are decades deep on the mic, yet with the best ghostwriters at their disposal, they often still sound stiff and sloppy.