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For the texture to show correctly, the mesh needs to be UV mapped.

Un-mapped geometry still has UVW coordinates. They are all just "0".
You created a new piece of geometry, assigned it a new material (without UV mapping).
When you applied the diffuse texture you saw the geometry change color.
What color is it?
Open that 2D image in a viewer and zoom way in to the upper left corner of the 2D image.
I'll bet whatever the color of the very upper left-most pixel in the texture, was the color of the geometry.
That's because all the UV coordinates are set to 0,0... ( the upper left corner of UV space).. and that's where it will get its color from the 2D image... the single pixel in the upper left corner.

When you create a mesh, all the vertices in that mesh actually have six (6) different coordinates.
There are the 3 world space coordinates we all know and love... X, Y, & Z...
Each vert also has texture space coordinates... they are labeled U, V, & W.
What most refer to as "UV mapping" is technically "UVW mapping". But, since the process normally puts all the texture space coordinates at W=0 (flat 2D space), we ignore W and just refer to it as UV mapping.

All U, V, & W coordinates have values in the range of 0,0 to 1,1. U,V=0,0 is usually the upper left corner, and U,V=1,1 is the lower right corner. (A few apps out there are different, hence the need to "flip" textures for transfer to some apps)
This means that you can map to a low resolution texture (e.g. 256x256) so the scene remains responsive in the viewport, but at render-time, swap it out for a 2048x2048 texture and, as long as the aspect ratio of the image remains the same (in this case -> square 1:1), the image will map correctly to the mesh. In other words, in UV space, 0.5, 0.5 is the exact center of the 2D image, wether that image is 32x32 pixels, or 4096x4096 pixels.

pokyking said:

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Did the selection take the colour of that pixel just because I hadn't clicked UV Mapping for those faces?

yes. The default UV mapping is all UV coordinates are set to 0,0 (the upper left corner of UV space).
I know that to get to the 2D UV view in wings you have to click thru the UV mapping dialog (e.g. "Continue -> unfolding"), so at the point you "continued", you applied some form of UV mapping.

pokyking said:

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though now as I type it, it seems almost impossible to fit that selection on 1 pixel.

0,0 is 0,0... it is an absolute and the UV points are, in the classic sense, "points", in other words... infinitely small.
A pixel, however, has a finite size in UV space. If the texture is 2x2 pixels, each pixel is 0.5 "UV units" wide and tall.
In other words, any UV coordinate that falls within the range of 0,0 to 0.5,0.5 would fall in the upper left pixel of a 2x2 pixel texture.
(Remember, all UV coord's fall in the 0,0 to 1,1 range...normally. As with most things, there are exceptions... tiled textures are one, but that another conversation, too )
The finite width of a pixel in UV space decreases as the number of pixels in your texture decreases.

pokyking said:

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Why would they even bother having a third axis in UV Mapping (the W)

Because some types of materials (procedural materials - "coded" materials as opposed to images) , can vary with depth.
In fact, in 3dsmax, the UV mapping modifier is actually called the "UVW " modifier, and UV editor is labeled "UVW Edit"
Look at the name of the window in this pic of the max uv editor, also note the direct data entry boxes at the bottom for all 3 texture space axes...
http://forums.filefront.com/attachments/sw-jk3-modding-editing/47125d1141538431-simple-sword-modelling-tutorial-3dsmax-gmax-u1.jpg


Wings does not allow editing texture space coordinates in the W dimension, but other apps do.

pics would help us troubleshoot a lot.