For one thing, it's probably much harder for these types of moves to make an impact when your stereotypical HR drone is handling incoming resumes -- hell, I can practically see them filing the cover letter in the standard way, the resume in the standard way, and the random hunk of metal in the standard way (garbage).
True, but then if it's a 10-person startup there's also the danger that they're so amazed by your ingenuity they decide they definitely want to hire you as soon as they've closed that next round so they can afford a few more people.
Now it might be the case that you're so engaged with their mission you want to wait a few months for a below market salary offer (hey, you're obviously far too keen to negotiate it) but it might be a trick that's easier to consistently pull off with a maverick-friendly businesses with more substantial funding or revenue
In my experience, your typical startup has its own drone handling resumes. It may not be a dedicated HR person—it could even be a fellow developer—but it's still someone with their own biases and blind spots. Engineers can certainly better understand how the demands of a position map to a candidate, but there's a tendency to "hire someone like me" that doesn't exist to the same extent with dedicated HR people.
Young engineers normally have more responsibilities at a startup, more trial by fire. It's great fun and good for career advancement.
There are tons of reasons for and against