I think the article is saying that EBS comes with no throughput guarantees (or even estimates of what to expect)
I've built block devices using the highest IOPS (fulfilling all the necessary requirements) at well as extremely large block devices (64TB) using EBS. When maxxed out and tuned to the gills, it's fast and big.
Genuine question: How is it cost wise, compared to other solutions you have experience with?