Nope, that can’t be it. Most of the single-engine airplanes I’ve flown have the landing/taxi lights in the front. I can only recall one with the lights in the wings. Never been in one with those lights on the landing gear, though I won’t say such don’t exist.
So I’d guess there’s another reason. Which may be as simple as “that’s the way they started doing it, and it got fossilized into the regs”
Yep you’re quite right, I forgot that a lot of singles have the lights just under the spinner. Spent too long flying things with the lights in the wings.
And of course I’m going to come along with an exception to the “position lights in the wingtips” rule. 
It’s almost comical, actually: the F-16 has missile rails on it’s wingtips, so you can’t put a light out there. But even F-16s have to comply with international aviation lighting rules, so the lights have to go somewhere.
They put the lights on the engine inlet!
For a look at the left, port, red light look at this. Look on the engine inlet just behind the pilot, lined up with the rail in the canopy.
For the starboard, right, green light look here. Same place: on the inlet, about lined up with the canopy rail. You can see the greenish color better in this picture (except for Broomstick who might be seeing some neon glow) 
Actually, “aviation green” is indistinguishable from sky blue for me. YMMV. Fortunately, taxi lights are an entirely different color of blue for me, otherwise nighttime airport manuvers might be even more challenging than they already are 
IIRC, this is also a handy traffic reminder. If your vessel is converging with another at right angles, and the other vessel is on your left, you see his green light and he sees your red light - you go, he stops. If he’s on your right and converging, you see his red light and he sees your green light. You give way.
This is more practical with ships than with aircraft, I expect.
From this page:
