I used to have the same problem starting out untill I saw a video of someone bending the string real far. Turns out thats just how far you have to bend for it to sound a full step up.

Try this out:

Use the 3rd string, 12th fret, which is probably the easiest to bend (kinda hard to control since its easy to bend to far aka sharp) Use your middle finger on the 12th fret, and your index on the 11th for better support. Play the 12th fret, then play the 13th. Then play the 12th and bend untill it sounds exactly the same as the 13th. That is bending a half step. Now do the same, except do it with the 12th and 14th frets. This is bending a full step.

As ren said, electrics are a lot more touchy since its amplified, but it is still highly do-able on an acoustic.