Indeed, this is true.
In a previous life I used to speak with the design experts and marketing people at Ansell, London Rubber, Sagami and the other large condom manufacturers.
Partly it's a marketing thing. (Which man is going to ask for 'small')
The vast majority of condoms made in the world are non-branded and distributed by healthcare charities. Condoms designed for use in Asia do tend to be slightly smaller than ones aimed at Africa, but not by much.
And besides, the rubber is (surprisingly enough) quite elastic.