If you seriously want to consider how economic trends impact musicians and bands - then you have to include the television and other streaming medias into that equation.
Live and DJ entertainment is easily and more profitably displaced by sports and other televised entertainment. Today is Super Bowl Sunday for example, who the hell needs a DJ for that?
I had an incredibly successful run with karaoke and karaoke rentals until the Boston sports teams started winning. The week the Red Sox entered the championship on their way to the first World Series appearance in 80 years - I got 3 cancellations. All were corporate events in bars or restaurants that chose to make the televised games the focus of their entertainment.
The bruins recovered their fan base with the Stanley cup, and the Patriots put the final nails in that coffin, repeatedly. The Pats have essentially become the center of entertainment in this area for the last 17 years.
Depending on where you are in the country there can be a variety of things that displace a given type of entertainment. Disc Jockeys in general are becoming a dated form of entertainment in the wake of American Idol and the incredible wave of exposure and interest reality TV has brought to diverse amateur and new talent.
There will continue to be needs in the wedding and other personal milestone areas, but in the general business arena I don't see a lot of opportunity for growth or expansion with respect to DJ based entertainment. It is a declining arena IMHO moreover due to changing social trends than any serious financial hardship.
Even when people cite cost as their reason it is more likely an instance of comparable expense and swap value not necessarily a true budget limitation.