How to understand Output voltage gain graphics

[screwdriver]

I'm trying to make a simple cheap amplifier for my computer sound card and whatever I do I get more puzzled. I would like to make a "decent" amp and when I saw the gain vs frequency graphics I couldn't understand these big differences, could someone explain?

As you can see from the datasheet LM386 and LM384 seem very flat up to 10 kHz, I would qualify this as "good", but what happens with LM 1877? what does it mean a gain that falls linearly?







The puzzle goes on: TDA7265 seems to be beautifully flat at frequencies over 200 Hz, while TDA 2006 and TDA2030 are flat up to a point in tha hundreds of Hz and then fall linearly, again in Gv instead of dB.