Well bulk can definitely be a decent deal depending on the seller and strain. But like Lodur said, you're paying for convenience, shipping and the risk that both parties (namely the buyer, but still) take. Maybe buying flowers off of SR isn't exactly worth the risk, but there's definitely many other options in the cannabis department, like concentrates, oils, etc.

Plus, there's every other drug on there like LSD and MDMA, and then pharmaceuticals if you fancy that. That's where the silk road really shines IMO, because personally, I rarely have quality or solid access to concentrates and other drugs.

Edit: Went off on a tangent a bit... Yes, maybe they do overcharge on a gram to 1/8 or 1/4oz scale. That especially depends on your area and connection as I'm sure you're obviously aware of. If you're from an MMJ area, then yeah I doubt it'd be worth the price/risk. However, if you're from say where I am from (suburbs of Philly) then maybe it is worth the price/risk.

Either way, have a look around the silkroad, I like to windowshop haha. Unless you already have and have made up your mind, then more power to ya ;)

Edit2: Or maybe I'm just high, so you'll have to excuse my book of a response, because maybe your question was somewhat rhetorical and I just can't handle the responsibility of this right now.