Single vs. Multi vendor approach?

Traditional consulting firms align themselves with a single vendor and tend to focus on narrow offerings tied to their favorite vendor, ignoring the opportunity to provide customers with "best of breed" technologies that might greatly reduce the cost of the network design, and deployment while further benefiting their customer. However,
both the approaches, whether single vendor or multiple vendor would be appropriate, depending on the individual co's resources and outlook.

The advantages of using a single vendor are:
1.It's easier, logistically, to deal with one provider.
2.When there are problems in a multi-vendor environment, one vendor tends to blame another. Single vendor approach eliminates finger pointing.
3.It alleviates support and training woes.
4.It can save you money. Spending more money with a single vendor may mean big discounts.
5.It streamlines network management.
6.Reduced procurement effort.

The disadvantages of using this approach are:
1.Losing ability to shop around for the best deals.
2.Lack of power to negotiate lower costs.
3.Losing awareness of new technologies on the market.
4.Being too risky for a company to have all its eggs in one basket.
5.Can be forced to upgrade products according to the vendor's schedule instead of the company's own needs.

(The advantages of single vendor approach could be taken as the disadvantages of multivendor approach, and vice-versa.)