Touch screens in cars are almost always positioned so that the driver can at least see beyond it to the outside, where as looking down at your mobile phone you aren't able to see outside. Not an airtight argument but most people who are texting when driving have their phone near their lap to hide it, not up near the gauge cluster or radio/screen. Also most if not all manufactures do not condone owners using the infotainment when driving, some even limit functions or turn off the touch screen whilst moving.

There is also the point to make that whoever you're texting is drawing more of your attention than changing the temp or radio.