Yes, we do have features that let you manage and approve vendors and multiple approval workflows. Invoice management is on the way. What procurement systems were you thinking of?
You guys are on the right track, but eventually you're going to hit a wall where you'll need some serious maturity with procure-to-pay.
I'm not sure how the tone of this comes across, or if it's in any way negative because you guys are onto something... but have a lot of competition that is often deeply integrated (see Service-Now catalogs for example).