Nothing new here.
Anyone seriously into benchmarking or high performance applications would know that raid controllers has been a bigger bottleneck than the harddrives for ages already.
It's just the last 2-3 years or so that you have gotten raid controllers fast enough to properly deal with the performance of the 6 tp 8 15k rpm drives that a normal 2U server can hold, and still today, many of the server raid cards out there still cannot do this.
Raid card performance has easily been the biggest differentiator on server performance for anyone that needed a reasonable amount of I/O capacity on their servers. Most servers have been reasonably equal in terms of memory and network performance. After all, they are all built around a very limited number of CPU and chipset architectures and there is only so much that can different there and it is a long time since gigabit network HW for server did not manage to fill a gigabit link.
Raid cards on the other side has major differences in architecture, software and processors. Proper HW raids are basically small computers on a card. They got their own CPU, memory and OS. This isolate them from the host they are plugged into and protect the data even if the host crash (the raid card will normally not crash and has all data in the battery backed up cache, which means a great deal for critical data and massively reduces the chances that you need to do consistency checks/validation and rebuilds after a crash on the host server which is equally important for a server).
Unfortunately as a result of all that extra complexity, you also get the potential for large performance variations between different raid cards.
When that is said, a good quality raid card now definately help on performance in most scenarios and easily outperforms software raids for most server usage that includes a reasonable amount of writing as long as you got that battery backup on your cache so you can safely enable write back caching.
Just do your homework and make sure you get a good card when you shop. The better cards can easily be 2-3x faster than the worst.