no drip leg on water heater

my brother recently had a new gas water heater installed by a well known plumbing company. when I looked at the install I noticed the guy installed the tank with a s/s flex line fastened to the vertical black iron pipe just under the union with no drip leg like it was previously plumbed. is it essential to have a drip leg installed on the black iron pipe like it was previously.

For practical purposes, probably not. From a code viewpoint, maybe. In most places, today's gas supply is quite clean, but it doesn't hurt to have a trap or drip leg.

I haven't installed a "drip leg" in the past 40 years, since I have moved to this area where they are not code required.