Antonia Beggs, the event's operations director, said the widely criticised fee was introduced after the 2006 Ryder Cup in Ireland.
She said: "The K Club was a fantastic venue, but one of the key issues was that the volunteers didn't necessarily stick around to do their crowd marshalling jobs all day.
"After the event, we sat down with the chief marshal and our volunteer co-ordinators and they said the only way we could sort it out was by introducing a registration fee. That separates the genuine article from the rest.
"My job is to deliver an incredible spectator experience, so I want to get the best people as volunteers. I'm not remotely concerned what their age or background is so long as they deliver."
The tournament, to be held at Gleneagles in Perthshire next year, brings together Europe and America's finest golfers from September 26 to 28.
The 1800 volunteers now being recruited are being asked to stump up the £75 fee, which is said to cover expenses such as the cost of their uniform and food.
Last week, Labour MSP Patricia Ferguson said the fee would exclude many young Scots.
Stephen Boyd, assistant secretary of the STUC, said the scheme was "unacceptable" and designed to attract middle-class recruits.
However, despite the negative publicity over the £75 registration fee for the event, more than 8000 applications were received on the first day alone. Applicants will be told if they have been successful in mid-April.
Ms Beggs added: "There was negative publicity over the £75 fee, but it wasn't coming from our volunteers or golf fans. More than half of the applicants have been Scots, with the rest from 46 other countries, including one from Equatorial Guinea."