I agree that these are different than stock options, but I have to say I still look upon this as more than "found money." 401(k) matching is part of compensation. A company is not required to provide it, but once provided, ownership of that money belongs to the employee, not the company.
The employees were sold a bill of goods at Enron. They were told they were getting something for retirement.... Actually, they were used to help ensure the executive team's lucrative exit. Is it illegal? Probably not. Is it immoral? I have little doubt.
The key here is that the purchase of company stocks was a condition of the company providing the matching funds in the first place. In other words, the "compensation" was ultimately not supposed to be a cash contribution to the employee's 401(k) account, but a contribution of X shares of Enron stock.
It looks like the executives at Enron have simply exploited a gaping loophole in U.S. tax law. Suppose Enron stock is trading at $100 per share. If the company had a profit of $10 million dollars, they would have been forced to pay a substantial portion of it (say $3.5 million) in corporate taxes or paid it out in company dividends (where it would be taxed at individual income tax rates that could be as high as 39%).
Instead of exposing themselves and their shareholders to that kind of tax liability, Enron simply paid the money to their employees on the condition that it be used to purchase Enron stock. The $10 million "investment" in the company drives the stock up to $105 per share, at which time the executives sell off some of their stock at the higher price. The money they make on the stock sale is taxed as a capital gain, not income, which means that anyone holding the stock for more than twelve months pays no more than a 20% tax on their gain.
The employees have been exploited here in a sense that they thought they were getting much more than they actually received, and there was probably some kind of fraud involved if the auditing firm gave the company a clean bill of health. I would need to know exactly how a top auditing firm could screw this up so badly before I could say exactly who was at fault here.