As with everything else in life, there are no absolutes. Here's where a speaker designer might use a crossover with a "hole" in it -
http://www.eminence.com/img/curves/Delta_Pro_15A.png
This is the frequency response for an Eminence Delta Pro-15A, a good 15" driver typical of what would be in a good 15" two-way speaker.
See that rising high end frequency response starting at 700 Hz? It's because of the electrical parameters of the driver, and is best fixed with a Zobel Network. However, instead of using extra parts,
almost the same effect can be achieved by simply setting the crossover frequency lower - only on the woofer - to offset it's rising high end.
What is not shown is that along with this rising high end, the dispersion is narrowing. Can you say "laser beam that hurts my ears", and is the main reason I don't like 15" two-ways. That's right, most of that nasty stuff is not coming from the compression driver horn tweeter, but from the 15" woofer, and is why the EV-SX500 has that disc on the grill*.
This problem only exists at high frequencies - crossing over from a woofer to a tweeter. No 15", 18", or even 21" woofer has this problem at 100 Hz. IMHO, what JBL is doing is still not logical.
*I shall preempt the miss-guided conception that modern powered speakers with DSP's can fix the dispersion problem. No, they can't, with the exception of Alto's, who use Unobtanium magnets, and operate outside the constraints of Newtonian Physics!!