Certainly, when receiving professional instruction, the modified car with at least an extra brake is typical. It's just that most people never get much of this instruction.
If you are under eighteen, states requiring driver's education from a professional driving school (with behind-the-wheel instruction): CA, DL, HI, ID, IA, KS, LA, MD, MA, MI, MN, MS, MT, NH, NJ, NM (waiver available), NY, NC, OH, PA, SC, TX, UT, VT, WA, WI,
Require the course, but not professional, behind-the-wheel instruction: CT, GA, FL, IL, KY, ME, MO, ND, RI, VA,
Professional instruction not required: AL, AK, AR, CO, IN, NE, NV, OK, OR, SD, TN, WV, WY, DC
So, about half of the country is required to have professional, in-car instruction. Quite common.
Still a huge number of people get no training and even in states that require training, it seems pretty minimal. 6 hours of driving instruction in my current state (WA) doesn't seem like a lot.