The wattage rating for speakers is a mostly useless term. It's not a recommendation for wattage, but a rough recommendation for maximum wattage. (Even at that, it's somewhat pointless as many more speakers are damaged by an underpowered amp driven into clipping than a more powerful amp that's not clipping).
It's important to remember that at most listening volumes, you're using under ten watts... very often under 1 watt. In reality, there's very little difference in volume capability between a 120 watt amp and a 240 watt amp.
Finally, it's the efficiency or sensitivity of the speaker that matters most. If a speaker is very sensitive, producing for example 96dB SPL with a one watt input, the needed amplifier wattage will be much lower than a less efficient speaker that maybe only produces 86dB SPL with the same 1-watt input.
It's more important, when trying to decide on a suitable amplifier, to look at the speaker sensitivity, room size and how loud you like to listen than to base anything at all on the "wattage rating" of a speaker!
