Well, just look at how linspace is implemented:
edit linspace
It might explain some of the behavior you see. On an additional note, comparing double value is risky business. Not only the way you perform a computation (as you so thoroughly illustrate) but the order in which you perform the operations will matter.
Even different compilers might give different results, since they might order operations differently. This means that you can potentially get different results in Matlab if you use different platforms.
EDIT:
As for the colon, here is how it is implemented according to the documentation:
j:i:k is the same as [ j,j+i,j+2i, ...,j+m*i ], where m = fix((k-j)/i), for integer values. For information on the definition of j:i:k with floating-point values, see Technical Solution 1-4FLI96. This syntax returns an empty matrix when i == 0, i > 0 and j > k, or i < 0 and j < k.
