I think it's the consistent daily doses of orals that make them seem more effective. Oil based are time released, but are not necessarily consistently dispersed on a daily basis due to injection site(scar tissue?)locations, etc.
However if you run oral compounds and take them daily at the same time everyday you can be fairly sure you're getting consistent amounts of AS in your system every day. I could be off on this? Just my theory. And btw-I think for the most part oral only cycles are not as effective as when combined with injectables.