When I applied for my Discover It I was instantly approved but with a shockingly low starting limit (10-15% of each of my other cards. Heck, it was half the starting limit on my very first credit card, which I got as a grad student with absolutely no credit history at all and an income that was less than half of my salary at the time I applied for Discover) and the worst APR I've ever been given. Tried to recon both and was told that I'd have to wait at least 90 days before requesting a CLI and wait until the 0% promo period had ended before requesting a APR decrease. 
Discover had me started with 25% of most other cards CL and stayed like this for 15 months... kept trying every 3 months for CLI with no success but on 15th statement got accepted for double CL and another 3 months later another increase and now it is pretty much in line with my other cards... With Discover you just need a bit of patience it will grow with time 
For me the reason for no CLI was my massive credit extention.. I added over 100K in less than 6 months and I can understand the concerns Discover had. To my surprise they finally did allow me to increase