What it actually did was kill the upper mid and high frequency echo that you're more sensitive to. The bass through lower mids is still 'echoing' (called ringing, long decay times, etc.) and muddying things up.
By treating only the upper mids and highs, you're not only missing a more important piece of the problem. Most rooms have a reasonable amount of items in them that are already absorptive in the upper mids and highs (think padded furniture, carpet, curtains, etc.) but very little that is good at controlling the bottom few octaves. Using things like foam are only skewing it farther toward being too dead in the highs and too live in the lows (including dialog).
Bryan