@David, @amirb, sorry to dispel your theories.
First, they did have equipment capable of producing such pulses with repetition rates well beyond 10MHz decades before the TDS3000 series was conceived.
For example, the Tektronix PG502, introduced in 1974, could produce such pulses with repetition rates up to 250MHz, and this is just off the top of my head.
Higher performing pulse generators existed well before the PG502
As for the theory that they simply wanted to use a specific calibration equipment, this also does not hold water since the recommended Wavetek 9500 can produce such pulses with a repetition rate up to 2MHz.
Finally, @amirb, you are confusing calibration with performance verification. The calibration process is not trying to measure rise-time or bandwidth because these cannot be adjusted.
In any case guys, all you need is in the manuals and spec sheets, so you don't need anybody's help, and can easily figure things out yourselves.
Good luck with your efforts!