Each type of ASP is tailor made for its specific clients. They are separate, but equal in outsourcing stature. Horizontal ASPs have honed their expertise in a process.
Vertical providers have a deep understanding of an industry.
It's their job to stay on top of the regulatory and tax quirks of an industry, like oil and gas or real estate, for example. They know their industries inside out. They are so specialized, no one else could really benefit from their offerings. Start up companies often select a vertical ASP provider because they need to outsource an integrated group of applications almost overnight. High growth companies favor vertical ASPs, too.