I think one thing to consider when saying WDW needs more roller coasters is not that they need more roller coasters, but more e ticket attractions. Lets see here...
Magic Kingdom has 3 E Tickets, Space, BTM and Splash Mountain
Epcot Has Mission Space and Test Track, and i suppose if you could soarin so 3 E tickets there
MGM has RnRC, TOT, and Star Tours 3 More
And Animal Kingdom has 1
For A Total of 10 E Tickets over 4 parks.
IOA has Hulk, Spiderman, Jurassic Park, Dueling, For 5 E ticket type rides
Universal has The Mummy... and Back To The Future I guess For 2
For A Total of 7 Over 2 Parks
Now Look at The DLR
Disneyland has Splash, Space (soon), Indy, Star Tours, BTM, Matterhorn 6 e tickets
DCA has TOT, Screamin, Soarin and grizzly for 4 E tickets
For A Total of 10 over 2 parks...
Now, maybe it's just me, but if your going to spend 53 bucks to go to any of these parks for a day, why would you go to WDW when you could go to IOA which has a better selection of rides?