It depends on the traders perspective. I don't usually base my rate on USD when I'm trading altcoin. I'm always using BTC as base currency so that my trading gauge will not be affected if ever the price of BTC drop or gains. A gain in BTC value is a good sign that altcoin price is really moving. Unlike if its only the USD price because its just the effect of BTC changing value not the altcoin itself.
Unless you're trading your alts for USD, then you and everyone else is doing this. Why would you want to even trade your altcoins for USD? The price of USD is locked. It's never going to move. Increase your position in Bitcoin and you have made a successful trade. Whether the price of Bitcoin has went up or down during the span of the trade, you're still successful in that trade if you made even a 1 Satoshi profit.