There are a number of other problems with pensions. The other big problem with annuities is that the insurance companies need a safe and steady method of payng the income. This means that they are low risk, low growth investments. With people living longer and longer after retirement, this creates a significant risk that your income will fall behind the real growth in the economy and earnings. There is more on annuities in Part 6 of the Fool's Guide to Pensions.
Pensions are also very inflexible.
However, this is a bit of a double-edged sword. It does at least force some discipline on you. If you think you're liable to blow all your savings at the drop of a starter's flag, then a pension could well be the way to go. All in all, there are as many different arguments about the pros and cons of pensions over ISAs as there are different types of pensions and ISAs. The important thing to take on board is that the decision, either way, is generally not clear-cut.