It's a factor one ought to consider - but at the salary ranges that we're typically talking about and at the typical match levels most employers offer, including 401K contributions doesn't change the math much, so it's mostly not counted.

For example, an employer who does a 1:1 match up to the IRS limit would be contributing at most ~$20K to your total comp, but when you're dealing with the rest of the package being in the $500K-1M range it tends to get glossed over.