I've been at jobs with small monitors and crappy chairs and I've been at jobs with small monitors and good chairs. I've also been at jobs with good large monitors and crappy chairs. If you offered me the choice of an Aeron Chair and a 30" cinema display, I'll take the chair. For software and network engineering related tasks, the single biggest enhancement of productivity is a good comfortable chair. The Aeron chair fits this bill.
But that doesn't, per se, mean that a good solid monitor isn't also a help. After 20 years in IT, I'd rate Apple in the top three for monitor quality.
I didn't say the Apple monitors weren't sexy! But $1800 is a big chunk of change for a startup. I have 2 22" samsung LCDs that cost $200 each back in 2007. Those are a much better investment in my opinion. My chair is an Office Depot task chair - $24 with $10 rebate in 2001. The chair comes with a warning: "not for multi-shift use"
Apple hardware (including 30 inch cinema displays), Herman Miller Aeron Chairs, and Glass Desks