Max. tyre width on racing rims

I’ve been browsing for a set of wheels. They’re going to go in a “road cross” (ie: not pure CX) frame, so I was thinking it would be nice to be able to run some fatter tyres for gravel roads, towpaths etc… I’ll probably go for a hand-built pair with Mavic Open Pro rims, but was also looking at Mavic Ksyrium Elite and Fulcrum Racing-3 2-way-fit. Mavic say that 28 mm is the max recommended tyre for their rims, but the consensus seems to be that CX types happily run 35 mm tyres with no problems. I downloaded the manual for the Racing-3s, and was very surprised to see that the permitted tyre width is only 23-25 mm, with a “danger of serious injury or death” if exceeded. Thinking it was something about the 2-way-fit rim I checked the manual for the regular Racing-3s, but it says the same. They all appear to be 622 x 15C ETRTO (ie: gap hooks inside the rim is 15 mm). Sheldon Brown has [url=http://www.sheldonbrown.com/tire-sizing.html#width]table of safe tyre / rim width combinations[/url], which suggests that 32 mm is fine for a 15 mm gap. So I guess I shouldn’t worry. Still, seems a pity that nobody does a 17C rim, which would be fine from 23 to 35 mm.