Re: Why not just buy a fully converged and integrated stack from one Supplier?
The idea of buying converged systems from a single supplier is often pooh-poohed as "proprietary", especially by suppliers who don't have the three technologies needed in-house, and the main three suppliers in that position are Cisco, EMC and NetApp. Both EMC and NetApp are trying to attract the attention of Cisco, the great converged stack prize, and hoping to be chosen as its preferred partner.
I think that might answer your question.
The problem with the "converged stack" theory is that it's the mainframe redux: you're locked into buying giant units of equipment from a single vendor. Virtualization ameliorates this issue somewhat, insofar as you can easily move your processing workloads elsewhere, but storage lock-in is especially pernicious since storage is the hardest resource to move away from. The discerning IT equipment purchaser will look for the opportunity to retain flexibility.
Also, take your Huawei shilling elsewhere.