It's standard practice in the US if you don't have a texting plan, or if you exceed your limit. Sending and receiving both count equally.

On most plans offered in the US nowadays texting is included. All of the T-Mobile, AT&T, Verizon, Straight Talk, Republic, etc plans have unlimited texting included.

That's pretty recent, though, and a lot of people are still on older plans. Still, it's good they're finally gaining some sanity there.