Any deployment of SaaS will require some services which are independent of what solution is being offered to the customer. For example, every SaaS offering needs to be able to do contract and subscription management, application and DB tuning, trial site management, application monitoring, security and client partitioning, etc. The SaaS platform companies offer to provide you with these applications and thus you only need to build the application you are an expert of. SaaSGrid and OpSource are two platforms currently doing the rounds. The links provide brief details about what these platforms do, but the basic idea is the same. In addition, Opsource tries to offer manpower as a platform offering, by doing support and application deployment when you buy their solution, interesting!
However, if you think about it, even though the thought is enticing (esp for companies who already have premised solution and want to quickly move to SaaS model), it is easier said than done. Most of the problems in SaaS world lie in creating an application which is order of magnitudes more scalable than any premised solution. Even though the problem seems to be something amenable to tuning of application-agnostic pieces (like DB, operating system, new hardware), real scale can come from an application designed to scale that way. Same goes for economy of scale, which is another important part of a successful SaaS deployment. This economy needs to be built into the application when scale grows rapidly.
However, there are indeed areas where SaaS deployment do get helped by such platforms. One such area is partner eco-system for services that all applications (or all applications of a class) need. For example, most applications will need payment and billing services, so will they need application monitoring services, customer tracking systems, helpdesk, managing trial sites, business intelligence and reporting, etc. As platforms mature and start creating such ecosystems and parternships, they will start becoming valuable. Till then, let’s wait and watch!