Precisely. If the signal is not there or weak to begin with, the amplifier amplifies noise. I've tried it myself. A waste of money. On local stations, you may overload your tuner too.
An antenna amplifier works best at the head of an outdoor antenna, to send the signal down the line.
Also, all antenna amplifiers are not of the same quality. On the Yahoo forum, someone pointed out some really good professional-quality ones that cost $150 and up. Much better quality than what you will find at R-S.
I forgot to mention the AuidoPrism indoor antenna which is amplified, but it is extremely expensive. One of the members here has one. An outdoor antenna, even of the most basic kind, will still outperform the AudioPrism.