I would agree that founders of a startup should be taking a relatively low salary. However, Buffer is no longer a startup (using Steve Blank's definition: http://steveblank.com/2010/01/25/whats-a-startup-first-princ...). It's generating significant revenue and is break-even from a cash-flow perspective.
Investors don't necessarily want founders to pay themselves the absolute minimum because they want the founders to be happy and focused on building the company, instead of being distracted by money worries.
Investors don't necessarily want founders to pay themselves the absolute minimum because they want the founders to be happy and focused on building the company, instead of being distracted by money worries.