The answer is likely quite simple.

Because allowing for one idea would lead into another.

70% tax is a start. Not the end. The idea is to find where the "excess" income is taking place and add additional taxes in that area to direct the income into investment and services.

70% may be a start at ordinary income. But does it apply to investments? And then what's next?

I think the key question for Dell and others is: can you show proof that the current approach of lower taxes boost the average individual income of workers? Because right now we're seeing great numbers from Wall Street, but wages are still virtually flat year over year. How does the Dow continue to climb but workers' pay stay the same?