It's not just about "having enough RAM". While that certainly is a factor, it's not the only one. As you suggest, pretty much everyone has enough RAM to run just about any normal application with 64-bit pointers.

But if you want speed, you also have to pay attention to things like cache lines. 64-bit pointers often means larger instructions are needed to be encoded to do the same work, larger instructions means more cache misses. This can be a large difference in performance.

I was curious, so I did some math:

320 miles / 15 gallons = 21.33 MPG
250 miles / 15 gallons = 16.67 MPG

320 - 250 = a 70 mile difference in performance.

At 16.67 MPG, 70 miles equates to about 4.2 extra gallons needed to reach 320 miles. So for that person, using premium is like having an extra 4.2 gallons in his tank.

In my state, the best prices I could find for 87 and 92 gas were:
$2.83 for 87 and $3.11 for 92

$2.83 * 19.2 = $54.34
$3.11 * 15.0 = $46.65

So for every 320 miles he drives, he is basically saving $7.69. Not earth shattering, but definitely a win.