I think the $5,000 limit on IRA contributions is too low also, but there is at least some logic to the way the IRS rules are structured.
Countless threads on DU have debated taxation of "The Rich" as well as the very well compensated. But the current IRS rules
do address this to a certain degree. If you make too much money, you can't participate in a 401(K) or use a Roth IRA at all, forcing you to use either traditional bank saving methods, insurance products (annuities, whole life policies, etc.) or traditional brokerage accounts. Regardless of how much you make, you can still have an IRA but you can't put more than that $5,000 limit into it each year. Tax deferred accounts are targeted at those people who really benefit from them the most, specifically people to whom the deferral of the payment of capital gains taxes to a later date makes a big difference.
Tens of millions of people (and many thousands of DUr's I would think) have regular, taxable investment/brokerage accounts. In such an account, if you make a trade that results in a gain from a security you've held less than a year, you are taxed at 35% on the amount you made. If you hold it a year or longer, you are taxed at 15% (it isn't completely that simple, but it works as a general rule. It's the IRS code, after all!). The burden of having the liability for that 35% or 15% each year is considerably less for someone who makes a very large salary as opposed to someone living paycheck to paycheck.
Have a look at
this web page. It shows the contribution and salary cap limits for the various types of retirement plans
If you'll notice, it states the compensation limits for being able to contribute to a Roth, 401(K) plans and SEP IRA's.
Individuals do have other avenues for putting away money and earning a better rate of return than a regular savings account but some of them have fees as well, like Annuities for instance. One could certainly invest in Municipal Bonds and realize a completely tax-free rate of growth.
I do agree completely that the $5,000 limit is too low, but how high to raise it is a serious question that warrants careful consideration. I think $20,000 is a fair figure, but it isn't really so easy.
From a standard of living perspective, we want to tax those the most who are least affected by the difference between making a lot of money and making a little less of a lot of money.