I'm aggree with the fact of keeping ppl from getting amp/dac more expensive than the 16/32 Ohm headphone they buyed, but solid-state amp can also color the sound. I have two motherboard: an Asus B85 with a classic audio electronic, and a Z97I-plus, were Asus used nichicon capacitor. the Z97 is more warm and laid-back than my B85.
Even on other website than head-fi i'm seeing a lot of ppl arguig about that one amp being able to smooth the harsh treble of a said can, or another amp to add some brightness to a veiled headphone. Other people are playing with op-amp to tweak the output to their liking.
It's only my opinion but if someone get a decent headphone,but don't have one of those new motherboard with "supremeFx", "crystal sound" "Audio noise guard" "Audio boost" , getting a dac/amp at 40-60$ won't hurt. When I've buyed my AKG K550 (300$ back then) all I had was a low end laptop with a cheap audio electronic. it's Only when I've buyed a great dac/amp that I've realised that spending 300 $ on Headphone wasn't the stupidiest thing on earth. I was like "those people getting excited for 1000$ headphone are just like those buying HDMI cable at 700 $. Placebo idiot".