That's true, up to a point. There are many antenna designs fpr receiving that are cut to specific lengths based on the frequency(ies) you want to hear. For example, one form of a true longwire (notice it's one word) is a wavelength or more in length, mounted fairly close to the ground. But if you're just getting your feet wet, using something like the PAR EF-SWL is a good place to start for HF (and yes, for some MW too, although on this band, loops rule).
Generally speaking if you want to get above 30 Mhz, it's time to start thinking about verticals, discones and the like. A wire antenna will work, but the efficiency is going to start to suffer the higher in frequency you go. At 144 Mhz, a horizontal antenna is very lossy (by about 20db) when listening to stations using vertical antennas.
The question remains as to what you want to hear, and where? Mike