why would they sell a 2A lamp switch?

[m_c]

You are over thinking it.

While you are technically correct, even a 2A rated switch will more than likely survive switching a load that will blow a 3A fuse.
You've got to consider what kind of load that's likely to blow a 1A fuse, but not a 3A, and not be noticed in a basic lamp?
L&N would need to be shorted together in such a way that they only drew 2.5A, and what is the real possibility of that happening?

The far more likely fault, is L and/or N wires rub through on something earthed, in which case it should trip the RCD. Even if you don't have an RCD upstream of your sockets, you should notice a fault before it even gets to the point of blowing a 1A fuse.