Sorry for the double-post, but I had another thought to help explain the difference between a 401(k) and a pension (from a high level).
All of the money in the 401(k) is the account holder's. It consists of funds deducted pre-tax (let's assume we're not dealing with a Roth 401(k) for now) from the employee's pay and may or may not include employer contributions. The personal money that one puts in ALWAYS belongs to the individual, and the employer contributions vest over a period of time from immediately to a few years. Usually, there is a percentage of vesting earned every year, so it's generally not an all or nothing thing. Say, for example, the employer contributions vest over 5 years. They will usually vest at 20% per year over the 5 years, so if the account holder worked at the company for 4 years, he/she would get 100% of the money they contributed and 80% of the employer contributions. At that point, all of their contributions AND the vested employer contributions are the employee's money. Therefore, this money can be transferred to other family members or anyone the account holder would like to pass them to. In the event that there are employer contributions that are not vested, that money is "deducted" (actually, it was never available) from the account.
A pension is totally different. It's a set amount of money over the remainder of one's life beginning at a certain age. There are probably different methods to calculate the monthly amount, but the way I'm familiar with is for the employee to earn a certain percentage of a salary (let's call it the highest yearly salary they earned for discussion purposes) per year up to a max percentage. So, in this example, if the employee earns 3% each year up to a max of 66%, and worked there 15 years, then the monthly amount would be 45% of their max salary divided by 12 to get the per month amount. This money is NOT the employee's. It is in the fund that is paying all the pensions and the payments will continue for the rest of the employees life, so there is no maximum payout (just a max salary percentage for the monthly amount), so that's why it doesn't transfer to family members outside of the spouse.