Do these bikes have freewheel hub or cassette hub? I am guessing the Bikesdirect bike has freewheel hub and the Trek 3700 cassette hub. Cassette hub is much better than freewheel hub.
Also, go to this website :
Bicycle Gear Calculator
and enter in the bikes' chain rings and cogs information, and you can see exactly what gear ratios each bike offer. I am guessing the 3X7 will give you a bigger gearing range than the 1X7.