Using an inflation calc [1] that amount from 1970 today would be worth approximately $6,273,872,679,045. So that would be $125,477,453,580 spent on R&D, and we actually spend close to $132,600,000,000.

So it's seems to have been a set amount just adjusted for inflation the whole time.

1 - http://www.dollartimes.com/calculators/inflation.htm