End Point Security - relying on one vendor's product a weakness in itself?

["secrookie () gmail com" <secrookie () gmail com>]

Our company is looking into using one vendor's product to manage our
workstations end-point security which consists of:

Antivirus/Spyware
Managed Firewall
IPS
Application Control
Buffer Overflow
Device Control (USB, PDA, Phones etc..)

My understanding with the layered security/defense in depth principle,
it would be foolish to go with one vendor's product as this creates
one point of failure.  If this product has a software vulnerability,
then the security of the workstations (and specifically the attack
vectors which the product is protecting) will be in jeopardy.  There
is no redundancy, its all or nothing so to speak.

Its like buying a Multifunctional Printer - if the fax or scanner
function breaks down, the whole device needs to be sent in for repairs
then you cant print.  Or if you buy the brand new Apple Time Capsule
for your backups, and the hard disk breaks down, you then need to send
the device to get repairs and would be out of WIFI for the duration of
the repair.

What do you folks think regarding the advantages/disadvantages with
depending on one vendors product for your Windows workstation security
in a global corporate (~50,000 seats) from a technical perspective?

I guess a balance needs to be met with the risks with putting all our
eggs into one vendors basket verses cost.