A few things
First interview person Henry Wertz: "The big one? Price; tapes cost about 1/10th the cost per byte of hard disks."
1.5TB Maxell LTO5 tape from Amazon: $67.95. 1.5TB Western Digital Elements external HDD from Amazon: $78.62. If you want to get really technical, you can get one of those HDD docking stations (similar to requiring a tape drive for tapes [which run about $2,600 for LTO5 btw]) and buy raw disk drives: Western Digital Caviar Green 1.5TB from NewEgg for $59.99. If you want to get really picky, you can assume no compression on the hard disk and an optimal 2:1 compress for the tape to achieve the 1.5/3.0TB capacity, then you have to get a HITACHI Deskstar 3TB (NewEgg $139.99), but mind you, compression on disk is quite easy and 2:1 is by no means difficult to achieve using even low on-the-fly streaming compression. Back up a video or JPEG library and you'll only see 1.5TB out of the tape. Therefore, even worst case (no compression for disk and optimal 2:1 for tape) lands at 2.06x the cost of tape. Best case is only 88% the cost of the LTO5 tape for like capacity. So no, not 1/10th the cost. Sorry. Especially when you factor in the $2600 tape drive vs a moderately priced Cavalry EN-CAHDD2BU3-ZB disk dock (for instance) at $64.99 @NewEgg.
Second interviewee Evan Unrue: "but also, disks keep spinning, so doing this comes with a larger physical footprint in the datacenter and a larger power bill. Tape scales by adding cartridges which don’t spin when not being use and don’t take up space in the IT room as they scale"
Why is it that everyone assumes that a disk-based solution mandates the drives are always on? Sure, the first target in the D2D2T or D2D2D will be required to spin, but not the last stage. Disks would work as removable medium just as effectively as tapes in this regard. I would suggest that disks are less vulnerable to environmentally-caused "bit rot" as well, due to the platters not prone to going brittle as tape has a tendency to do (at the very least it can withstand being in a less-than-ideal storage location better [think attic of IT Director's house or the like] if necessary).
I applaud the third interviewee Chris Evans for pointing out some of the shortcomings of tape solutions. Granted, disk has disadvantages too, and as Chris said, it comes down to finding a balance between the two based on your RTO/RPO requirements. The key is finding the best spot to use the appropriate medium. For enterprise environments with hundreds (or even tens) of TBs to backup, you can't beat a tape library for convenience. For anyone with 3-6TB or less for a full backup set, anything more than tape drive or external HDD is likely overkill, especially for the sub-1TB market.
As always, check your logs on your backup jobs frequently. If that's too much of a pain, find a way to have the results emailed (same as paged nowadays) to you upon completion/failure. For those willing to roll up the sleeves (such as the ZFS/CopyFS commenter above), there's plenty of methods you could employ to produce a better setup for your organization than BackupExec or the like could provide, and using HDDs just makes that solution even easier and more feature-full.