They are wrong about the threads operating on the same data. A naive reader skimming over the code may think most of the data is the same, but the 32-bit nonce is unique for each thread, which leads to different SHA-256 intermediate hash values (A-H) being manipulated by each thread.

Re: enterprise prices - it is truly market segmentation, whether you want to believe it or not. The 2 largest and public disk reliability studies ever performed were made by Google and CMU. They reveal interesting findings. In particular, contrary to what you think, the CMU one reported no statistical differences between the failure rate of SCSI vs SATA drives on a population of 100k+ drives:
* Failure Trends in a Large Disk Drive Population - Google
* Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you? - CMU
Which makes sense when you think about it. Commodity drives are produced in such a high volume that it is in the manufacturer's interest to make them as reliable as possible, because a small improvement in reliability drastically reduces the number of warranty claims.

This is just some food for thoughts... You should trust more of the people here. The Bitcoin community is full of smart folks. Open source has produced some of the highest-quality software in the world: Linux, Apache, etc. A miner is also just a few hundreds lines of code. It is not a complex, hard-to-optimize software beast that you may imagine.