It's probably the first time I've ever said this, but I am an expert on these machines, as I drive one for a living. One of the main reasons rinks still prefer natural gas (or even propane) is that those ice resurfacers have what are essentially internal combustion engines, which reduces repair costs, because the cities that own them usually have many spare parts around and the employees that work for the city usually know a lot more about ICEs than electric engines.
Further, eight years seems a little short for a natural gas machine; our last one (propane, actually) went 15-20 years (and we still use it to take out the ice in April and when our main one breaks down (man, it's a PITA to drive)) and our newer one is still going strong after nearly 10 years, and given its 3,800 hours of use, we probably won't be replacing it till near the end of the decade (barring unexpected problems), hopefully when electric motors are more competitive.
Lastly (not a reply to you, but to others), so long as your ventilation system is decent (which I would assume an Olympic oval's is), and it's actually used properly, air quality in an arena using a natural gas resurfacer is essentially the same as that in one using an electric resurfacer. If our arena didn't pass with the flying colours it got and instead got the massive fail 4 Glaces got I'd be suing my city (or getting our union to do it) immediately; I'm sure Olympic spectators have nothing to worry about.