First, I agree with the title being misleading, and I apologize for it. It was never intended to be a complete guide, which would be virtually impossible. I don't know why that title was chosen.
The choice of computers was U.S. centric, because computers were U.S. centric. I chose only one mechanical computer, and it was made by IBM, since they were the dominant company. To add more computers would have been boring, and none of them were important technological milestones. So, while they might be specifically interesting to you, I was of the opinion too many computers from the same time frame would be boring. I almost chose the EDSAC over the EDVAC, but, went with the first design over the first implementation.
With regards to the index registers, "the IBM 704 added index registers and a “TSX” instruction that would branch to an address but leave the address of the TSX in an index register. A single unmodified branch could use that index register value to return."
Loops involve branching, branching involves memory addressing.
With regards to floating point vis-a-vis integer, you need to be more careful about what you're sure of. For one, multiplies and divides are generally slower, being much more complex. But, more to the point, this information is available directly from IBM.