The incumbents also owe their livelihoods, or at least much of their government funding to the successful platform Tonks' athletes built over previous generations.
You only had to witness the compassion he held for Fiona Bourke, an incumbent women's double world champion struggling in the single at this year's Lucerne World Cup, to understand there is empathy beyond the gruffness.
"When I was fresh in the system, I'd heard stories about him being scary. I was terrified to talk to him but realised it's just that he takes his job seriously. He has great intuition for his athletes," Bourke said last year.
"Three months before I was coached by him [in 2009], I remember being in the summer squad a week before Christmas. I was awful in the single, so I decided to stay three extra days. He came down at 6am to give me a hand. If you are willing to put the time in, he will too."
Having heard both sides of the story, his decision to coach Chinese athletes leading into the final year of an Olympic cycle may have been ill-advised. There is an argument Tonks benefits from the taxpayer, and that demands blind patriotism. However, he has also given New Zealand sports fans a return on investment through the joy of countless world championships and five Olympic gold medals in the last four Games (his protégé Calvin Ferguson also coached the men's double to gold at London). You'd struggle to find a fan not moved when Rob Waddell's triumph avoided a national gold medal down-trou at Sydney, or when Caroline and Georgina Evers-Swindell won at Beijing by 0.01s, the only moment they were ahead in the race.
Tonks is New Zealand's most successful Olympic coach with five gold medals and a bronze from his crews. The late Arthur Lydiard picked up four gold (Peter Snell 800m 1960, 1964; 1500m 1964; Murray Halberg 5000m 1960) and one bronze (Barry Magee, marathon 1960). Boardsailing coach Grant Beck has three gold (Bruce Kendall 1988, Barbara Kendall 1992, Tom Ashley 2008), one silver (Barbara Kendall 1996) and three bronze (Bruce Kendall 1984, Barbara Kendall, Aaron McIntosh 2000).
For Tonks, a man who knows what it's like to finish second on sport's greatest stage in the coxless four at Munich, there is no substitute for practice. As a 21-year-old he was confronted with the fine line between winning and losing in the toughest way.
"I don't think there's any such thing as talent [at the professional end of sport]," he once said. "Those who are good at something from a young age often don't go on. If you think you're good and things are easy, you're never going to get there."
Anyone who has been out in his coaching boat will understand his mesmeric qualities of persuasion. He constantly murmurs constructive observations into his trusty megaphone: "Hooold the catch, niiice and relaxed, eeeasy on the oars," emphasising the first syllable.
Tonks has the ability to pick up idiosyncracies and flaws within the rowing stroke as well as anyone in the world. He is a voracious reader and researcher on his area of expertise - anything to make the boat go faster. He can immediately see if the catch of the oars in the water is not maximised or if a rower's muscles are under-used in a certain area. He liked the fact that when rowers came into the squad, they assumed they were good enough to medal.
"The culture has built slowly through winning," he said before the London Games.
"Anyone who joins this programme has to believe they're good enough. That means they don't sit on the start line, look across at the Germans, the British, the Americans and the Russians and think, 'Aw, hell'. Those other crews have to look at our black singlets and know they're going to be under threat."
He would tell the Evers-Swindell twins they weren't judged on how they competed. It was about being quickest between A and B. He would then hold his thumb and forefinger up with about one centimetre between them and say, "It could be this much". The 0.01s margin in Beijing vindicated his point.
As he has put it: "Ah yes, sitting on the water waiting for the boats to return; it beats pushing paper in an office."
Unless there is a monumental volte-face, those days are over. New Zealand international crews might never benefit from that wisdom again.
Still, as with any such decision there will be a bright side. Tonks' wife Flo and their young family, who live on a farm near Cambridge and occasionally joined him on tour with the help of Rowing New Zealand, may ultimately benefit.
