Hsu again cites only Mahoney for this, and the passage here is presented as one quote, but it's actually a quote within a quote: first Bemer and then Mahoney. The original Bemer quote ends with the second sentence ("I contend that the production
costs are affected far more adversely by the absence of such an environment than by the absence of any tools in the environment…" which ends prematurely here but ends with a parenthetical "e.g. writing a program in PL/1 is using a tool"), and the remainder is Mahoney's commentary.
The Bemer source is:
R.W. Bemer, "Position Paper for Panel Discussion [on] the Economics of Program Production", Information Processing 68, North-Holland Publishing Company, 1969, vol. II, p. 1626.