As blhack pointed out Voxel's per-GB rate[1] before AWS dropped was extremely competitive, but they charge for in and out-bound data. AWS, after the 1st of July will only charge $0.12 for out-bound data and $0.00 for inbound data, effectively making it something like $0.06/GB compared to Voxel (I'm hand-waving this a bit to make a point).
Also as wiradikusuma pointed out, this comes right on the heals of Google's App Engine pricing structure change[2] to be more business-friendly (read: more expensive/more predictable billing) that upset smaller shops and individuals.
As someone who reads most of the AWS forums every night, I would say overall that Amazon seems to be responding more quickly to low level failures that used to run rampant on the system (although US-EAST still has more failures than any other region. I guess due to overload). They seem like they are hitting faster/smoother, sounds like a good time to push forward and grow which I imagine this move will help do.
Getting a little excited to see what the price decrease for per-GB billing on S3 will be in the coming months following this up (my assumption).
[1] http://www.voxel.net/pricing
[2] http://www.korokithakis.net/posts/app-engine-pricing-changes...