Did you get a midbass driver and a tweeter with those, Chris? Or did you just get a midbass? With components, you want to only allow certain frequency ranges to each driver (high frequencies only to tweeters, mids only to midbass), which is why you need crossovers if you have more than one type of driver running off of a single amp. With most amps, (actually I think all) you can set a cutoff frequency for the output, which makes it kind of like a crossover, but without actual crossovers, you end up sending all the non-cutoff frequencies to all of the drivers, which can damage them/waste power/make your music sound bad.
For example:
If you have tweeters and midbass drivers (a typical 5.25"/6.25" component set), but you have no crossover, in order to get anything out of the tweeters, you will have to set your amp's crossover to full range. This sends very high frequencies (10,000 Hz+) to the midbass drivers (which they cannot reproduce), as well as lower frequencies (less than 500 Hz) to the tweeters, which they cannot reproduce. This can damage your drivers.
This is where crossovers come in. They take a single input line from an amp, run it through some capacitors, and split it into two or more outputs which only have certain frequency ranges in them. Then these outputs get connected to their respective drivers, and everything sounds great.
I have never seen a component set that did not come with crossovers though... Did you get a component set?
Sorry for the long post... I hope it helped you though.