The same thing is true of many good headphones in the $200 - $500 range. They tend to be higher impedance, so they need an amplifier to really perform. Maybe it doesn't seem so bad to pay extra for an amp for a really expensive headphone, but as you say, if you buy a $150 headphone, you might end up paying more than that for an amp.
The way I look at it, though, is the amp and the headphone are separate purchases. If someone is just getting into better-quality headphones, maybe something like this DT990 Pro 250 ohm is their "gateway" to higher-end headphones. Maybe they have to buy an outboard amp for $150 to $500 more, but then they can continue to use that amp if they move up to even better headphones later.
I didn't really appreciate my Sennheiser HD580s until I plugged them into studio gear that had strong output at the headphone preamp. They improved even more with a dedicated, standalone amplifier.
Lately, there are some good, high-output headphone amps for not too much money. I've been meaning to create a new topic about headphone amps, and I guess this is a good time to do so. I'm off to do that now!