That's somewhat a fair point, but I'll disagree.
In that instance, the co-founder replied, but I've heard from a number of Stripe's other employees since then, and in every case the customer support has been wonderful. Perhaps that's solely because they are still a startup, but given what I know now about the people themselves, I don't believe that to be the case.
I don't mean my original comment to suggest that the co-founder will always be the one to respond to a tweet as Stripe grows, but I do suspect that their standards for customer service will remain high, and someone in the company will give a quick and quality response. That said, with Stripe, I believe that–even if they aren't the ones responding to every tweet, which is admittedly much to ask–the co-founders will continue to have an eye on what people are saying about them and interact appropriately, not wall themselves off.
Edit to reflect your edit:
I remember that HN thread where you brought up chargebacks. For anyone interested, they discuss how they handle chargebacks here: https://stripe.com/help/chargebacks
I can't attest as to why they manage chargebacks that way, and will not speculate beyond the note that they are still new and seem to be developing their service in response to customer feedback and perceived needs.
For you, or anyone else who might be interested in requesting features regarding chargebacks or any other aspect of their service, I highly recommend writing in: support@stripe.com or https://stripe.com/help/contact. As I mentioned, they're very responsive, and seem to love the feedback.