So much of it depends upon your room size and how loud you want to listen. Obviously the larger the room, the more power you will require to fill that room. The same for high volume listening. If you are using a smallish room and never go louder than 80dB, then you really don't need too many watts. BTW, 80dB while not considered loud is too loud to have a normal conversation. The manufacturer's suggestion is a generalization to cover a wide range of situations that may or may not apply to your particular case.
how can low watt tube amps drive speakers with higher power requirements
I am new to hifi and I am super confused about something. Most audio blogs out there ask newbies to stick to amps that output power within the recommended range of the speaker manufacturers. However, on forums, blogs and even some magazine articles, I find pros reviewing tube amps with much lower output power (even in some cases 10-30W below the speaker specs) and find no problems. How can these low power tube amp drive these speakers? For example, the LS 50 metas spec sheet says "Recommended amp power: 40W - 100W) but I have seen posts here and on other forums where people will hook these up to tube amps producing as low as 12W of power at 8 ohms. Am I missing something?