First of all, let me say that the folowing is not just "sucking up;" this the general philosophy that I believe would apply. I like Extreme switches and their support organization, I've worked with them on a number of occasions and every time was a positive experience.
All that being said, the reason you'd decide to buy Cisco over Extreme would be the company and the support organization.
There are very few (actually, none) vendors / producers of equipment that can compare to the scope of product offered by Cisco. You can do virtually anything network-like and still be using Cisco equipment (i.e., voice, video, data, streaming content, content delivery, firewalling ...).
The advantage in that is maintenance and support. You only have to go to one company when something goes wrong. Since everything comes from one company, there is little / no finger pointing ... everything is Cisco, Cisco will get it fixed.
From the on-going maintenance perspective, you only need one monitoring platform ...
From a support / update standpoint, you only need one contract for all software updates / upgrades.
Since you are purchasing equipment and contracted support,budgeting is much easier.
From a training persoective, it is much easier to find someone (pre-trained) who is Cisco qualified, and it is much easier to find someone you can train you on Cisco. Go to the book store and try to find a book on "Everything (anything) You Ever Wanted to Know about Extreme Switches" ... I've looked, I've never found ONE book on Extreme. Look around and try to find online forums that handle Extreme questions or discussions (virtual NIL) versus site that have information about Cisco (the company and / or equipment) ... there's hundreds / thousands / tens - of - thousands.
If you were asking specifically about those particular switches, you are comparing apples and oranges. The Alpine / Black Diamond are chassis-based switches, the 3750 is a (for lack of a better term) stackable ... more comparable to an Extreme Summit.
The answer doesn't really change though: you buy Cisco equipment because of the support and the company.Their reputation (way more often than not) is for outstanding service and support.
None of the above is meant to imply in any way, shape, or form that Extreme is not a great chunk of hardware ... personally, I love 'em. For a company to decide to use Extreme over Cisco, they must be willing to depend on Extreme for any and all resources (since there aren't any books, aren't many websites / forums, and aren't many pre-trained folks on the street).
I hope I answered your question.
Good Luck
Scott
