You assume that the hardware implementation would not have to do the same thing: use the framebuffer clearing mechanism to clear the texture's data. Remember: doing an actual clear like this on texture memory is not exactly a common operation. 99 times out of 100, if you're clearing an image, it's because you're about to render to it. Textures not meant to be render targets are typically uploaded to, not cleared.
It just is awkward.. also affects GL state and obscures what I am after: memset a texture.