Ahh, economics. I am no economist, but I'll try to break it down for you.
As I already mentioned a few posts above, Pakistan has two developed states: Punjab and Sindh.
Looking at the demographics:
Punjab
Total share of Pakistan's GDP: ~55%
Sindh
Total share of Pakistan's GDP: ~30%
Rest includes North west frontier and Blaochistan
Look at this chart.
Now as already mentioned above, POK, NWFP and Balochistan are backward regions.
The Pak Govt has virtually no control over NWFP and Baloch. It follows ago old system with tribes, village elders, etc. Since 2001 there is huge inflow of terrorists from Afghan.. and the ISI funds extremists in POK.
Now there is growing influence of Taliban and Al-Queda in those backward areas.
Al-Queda is training people along the border and inciting violence in the relatively peaceful area of Punjab and Sindh. Add to that, there is sectarian violence against Shia's, Ahmadiyya's and Sufi's.
OTOH, Pakistan's ISI is funding Violent Kashmiri Separatist movement(Reference available in wiki leaks documents).