not just CRM sites do this of course.
I get that macs are more hip than PC's, but don't most "real businesses" still use PC's? last time I heard macs were under 5% of the pc market.
Why do tech companies prefer to show their customers using macs?
http://gs.statcounter.com/#os-US-monthly-201211-201301-bar
Among certain groups it is higher; for example among college students, software developers (especially web developers), graphic designers, and advertising agencies. So part of this is that the companies producing the web sites you're looking at are simply using images of the computers they happen to be using.
Apple is a well-liked brand with a public image of luxury, polish, usability, etc. Companies probably want associate themselves with those qualities in their own marketing.
That is the simple answer. They have a more modern, sleek, look. Other companies like Dell are only recently catching up with them in terms of looks.
When I bought an aluminum unibody MacBook in 2008 I had a person who never used a Mac in their life compliment me on how slick the laptop looked after I closed it and got up to walk across the room.
Also consider this: Of what market research considers "luxury" laptops, Apple account for 9 out of every 10 sales. I.e., all of the other companies with what they present as luxury laptops accounts for only 10% of those sales. When you think luxury laptop, Apple dominates.
It will be interesting to see if this changes over time given that the perception is Apple is alienating this market in favor of the general consumer market. If true the observation of this topic may change with it. It will be interesting to see if the creatives are a silent marketing tool that Apple has overlooked in it's transition to a more general consumer company.