That was the head parking bug the early Greens had (which as been fixed). Parking every 8 seconds is a far cry from parking only a few times a day. In theory a HDD running 24/7 and parking the heads every 8 seconds would reach 300,000 cycles in only a little over three days. I had one of the early Greens with the head parking bug and it lasted a bit over a year while running 24/7. If one parks the heads only 20 times a day, in theory, the drive would take a bit over 41 years to reach 300,000 cycles. Reaching 300,000 cycles does not mean it will die then. It could die sooner; it could last longer.
That's more like 28 days and not 3 days. Every 8 seconds equates to around 10,800 load cycles per day. And you're right, as long as there's a reasonable wait time, there's nothing wrong with spinning down drives when idle. However, I do remember reading something in Google's whitepaper that drives with a lot of load cycles experienced more deaths than drives that were left spinning constantly.
Mind, the default Power Saver option in Windows puts HDD spin down after 5 minutes which is way too aggressive for my taste.