If you work for a large company it is possible that they have negotiated better pricing for their 401k plan than what Vanguard or some other brokerage offers off the shelf. For example Vanguard charges 0.08% for its target date retirement funds, but the one I get on my old employer's plan (BlackRock LifePath) is just 0.037%. And the retail price for that LifePath fund is a whopping 0.17%.
Usually when you leave the company they start charging a quarterly service fee. Be careful out there.
With how low fees have gotten, I think the more likely and more damaging situation is that where people's employers have negotiated much worse pricing for their captive audience. I wouldn't give 0.08% vs 0.037% a second thought any day. That's only difference of $400/yr on $1M!