Yes, it's pretty extreme.
But if you're not at least 6 feet / at least 2 inches taller than your partner in heels, any women you're with is likely to believe that she's compromising.
Having a tall boyfriend is also important not just aesthetically, but so women can brag to other women. I've been told by women friends that a common question they get whenever they date someone new is "how tall is he?" So other women know that too, that if they get a new boyfriend the first question their circle of friends will ask is "how tell is he?", part of them will want to bring in a man they can brag about, that their friends can tell them congratulations, and that none of her friends will believe she's compromising.
That's largely from a woman friend of mine, we'v been close for 11 years, who is 5'3, she's dated men 5'6 through to 6'1 I think, she doesn't particularly care, but she notices it in other women and speaks of it as if it's the most ridiciulous standard women have. She's told me that she thinks women are perfectly capable of loving a man who is their height or whatever, but a lot of them nevertheless have a 6 feet rule.
