Problem with 401K is that it's not inflation proof. Your Grandmother, presumably if she's old enough, likely remembers when she only paid $0.05 for a Coca Cola in a restaurant; whereas today, a Coca Cola costs up to $2 (if not $3 in a bar). Coca Cola increased 40 to 60 times within generational memory. The samething will happen to your 401K - it'll decrease in value by 20 to 60 times by the time you collect.
Pensions suffer the same issue too, I might add, unless you have an indexed pension like government workers. The reality is most of us will probably die from starvation in our old age due to not having any money, unless we manage to keep a job somehow.
That's the reality of inflation, folks. Back in the age of prosperity, when currencies did not inflate to the moon, it wasn't uncommon for people to retire in their 50s. It's a dystopian society if we are working people to death, especially when this is contrasted by all the Paris Hiltons and other capital owning parasites
The price of a soda varies very widely from restaurant to restaurant. The vast majority of restaurants also offer something called "free refills" today, while this was likely not the case when Coca Cola cost $0.05 (fountain drinks technology was not available at this time, and it was always sold in bottles), so when you pay "$2" at a restaurant you are really paying a total of $2 for as many Coca Colas as you drink while you are at the restaurant.
The value of 401k's is based on the investments in the account. It is the goal of these investments to beat inflation. In 1914 the Dow Jones Industrial average (DJIA) was at ~71 (for rounding we can call it 100), as of yesterday the DJIA closed at 16851.84 (call it 16,000 for rounding). This is a return of 160x verses 60x for your soda example (from 5 cents to $3 at a bar).