You're totally right that it has a generational component. But it's not just the generation of the company, it's the generation of the employee.

Consumerization (apologies for the buzzword) of internal business technology is an undeniable force that even slow-to-notice Gartner recognizes.

A few things are conspiring to help move Macs into the enterprise, even in older companies:

* the Internet. (the biggest reason of all. So much of info workers use all day is on the web. Good ol' I barely-care-what-OS-you're-on web).

* desktop virtualization like VMware Fusion made it so employees who could do 90% of their work w/out Windows, could still login to that one timekeeping app that required Windows.

* the iphone (especially) + android were so much better, so far ahead of Blackberries that Exchange-friendly connectors were written.

* BYOC (Bring your own computer) movement. Multiple enterprise IT departments, even in old school companies, are using a system where a stipend is given to an employee to buy his/her own computer.

* Google Apps (see also: The Internet). But more specifically, Google Apps dislodges the Exchange/Outlook roots that are the number one reasons big corps can't leave Windows.