That's the "put all 10TB on each streaming server" solution that he immediately rejected because of expense. You can see that the more streaming servers you connect to the storage system, the more important seek time becomes. He did then say "whatever architecture", which is not quite right since the seek bottleneck may not appear until the streaming:storage ratio gets higher than 1.
For a realistic exercise, throw a cost factor into your equation and optimize for cost and latency (aka user experience).
In the big picture, are the drives that expensive? Your monthly bandwidth bill is going to come close.
Measuring latency (vs seek time) is definitely a better metric. But is a 5 second (the horror!) delay to watch a 40 minute video that bad for user experience?
A better example may have been streaming music, where we already know last.fm got a big win from using SSDs.
The drive themselves might be an extra 10 or 20% of the cost of the machine. They come with other factors as well. 5x the disks means more power draw and cooling. It probably also means you need a 2U chassis instead of pizza-box 1U, which means your datacenter rent doubles. (It may be possible to fit 10TB into a 1U. I've never tried it, but I suspect you'll have space / power / heat problems.)
For a realistic exercise, throw a cost factor into your equation and optimize for cost and latency (aka user experience).