Relevant to Ric's post (and others on this thread), since there is no difference between liquid and dry ferts (N is N and still has to be dissolved in water before it can be used, so it doesn't matter if you apply it wet or dry), your customers' needs and the nature of your book of business will determine your equipment needs.
The big guys out there usually use liquid fert only when they need to apply pre-emerge products, since you can't customize your PRE rate independent of the fert rate with dry products. Outside of PRE windows, I see them use dry ferts.
So, back to the OP's question, can you develop and implement a granular only fert program? Yes! Several big name companies over the years (Barefoot Lawns, for example) made a lot of money and had high quality lawns with granular only programs. You can easily do fert and PRE on a granule. POST products, though, usually aren't available or effective on granules, though.