There are trends on how storage is purchased and a few of them are worth pointing out. One is that in the enterprise...
data center market segment, storage is purchased independently of the server for the most part. In that market, the storage purchase is centralized and done on a fairly regular basis -- usually once or twice a year. Usually a customer will purchase from only a small set of vendors at any one time -- two in most cases and only changes the vendor selection about every three years. It's pretty tough to break into that cycle.
In the small to medium-sized business market, the primary storage is almost always purchased with the server purchase, which is termed a "server-led sale." There is a secondary storage purchase that occurs and for the most part, the customer will purchase from the same vendor. But not always. There is great opportunity here for a vendor to make a sale with that secondary storage purchase. And it's a big market that is growing faster than any other for storage.
It is important to evaluate the storage products AND the storage vendor before making the selection. Buying storage at the same time as the server may not be the best move -- there may be a better storage solution -- but a package deal may make it compelling. I always recommend evaluating storage independently and not getting locked into a storage solution that might be a compromise.