Everybody knows tablet is easier to use, but why?

A tablet is a drawing tool, since this an animation site, they are usually easier to draw stickfigures steadier for animation.
Both tablet and mouse require practice, so it's usually preference, some people have difficulty adapting to tablet.

It depends... They have their own good points. With the mouse and line tool, you can have the smoothest stick possible.
With the Tablet and the brush tool, you can draw easier every position fot your sticks.
I used to animate with a Tablet, but now i rather the mouse and the line tool... Because when you zoom in/out, the brush changes size, so it's pretty annoying. Also, the line tool have more sizes.
The line tool keeps it size, it doesn't matter how much you zoom in/out. also, with the line tool, you can modify the stickman however you like with the selection tool. With the brush you can't, because it draws with bit maps.

The ultimate combination would be Tablet with the pencil tool (wich is a combination of the line tool and the brush xD) You can modify it, it doesn't change sizes when you zoom in/out, you can modify the stickman, etc. In brief, with the Tablet and Pencil tool, you have the better of both. I don't have a Tablet so i can test it xD

Its not like tablet is better per say
I guess its just a matter of which is easier to use/more time efficient
I would give that to tablet
You can be good with mouse, having a tablet doesnt automatically make you better.

Well, the tablet isn't exactly "better", it depends on preference. But if you're a brush animator who wants to make more precise and accurate positions for your sticks, then the tablet would possibly be a better choice.

I have an Intuos5, and it helps me draw and position my sticks more precisely than my mouse. But I'd recommend a cheaper Wacom tablet for starters. (I used a Bamboo Pen before my Intuos, and it got the job done just fine.)

I'd recommend the Bamboo Capture for people who want to begin using a graphics tablet.

The tablet was invented to be used to animate and drawing, it'll obviously be easier and more comfortable to use than a mouse.

I voted for the touchscreen laptop/ monitor. This is because I have seen some which you can flip around to be like a tablet. It is better than a tablet because you are putting directly onto the screen. With a tablet you have to use some (even though very little) hand-eye co-ordination. You won't be able to use pressure sensitivity though.

i think of a tablet as a pen and virtual paper (your flash screen). Tablet is like using a pen, it helps with drawings of art, full body,sticks and the rest. I'd go for the table that's if your choosing.

Quote from Camila

The tablet was invented to be used to animate and drawing, it'll obviously be easier and more comfortable to use than a mouse.

Yup. This.

Quote from flamr

I voted for the touchscreen laptop/ monitor. This is because I have seen some which you can flip around to be like a tablet. It is better than a tablet because you are putting directly onto the screen. With a tablet you have to use some (even though very little) hand-eye co-ordination. You won't be able to use pressure sensitivity though.

this.

this is what i use. Fujitsu T4220. it has pressure sensitivity but not tilt(which i found annoying since i spin my laptop a lot. and the pen/digitizer is made by wacom so there's no complaints on quality.