I actually find this quite irritating....
It's the same mindset that makes people assume that anyone who "works with computers" can automatically fix any computer problem. eg. "You're good with computers right? Can you fix uncle Gus's friend's of a friend's printer?" Urgh.
I guess the reason why "IT" is talked about as one big monolithic field is that it's still relatively young. As little as 20 years ago, computers were still a fairly esoteric thing. Being "in IT" was a fairly niche field. As it expanded and became more specialized, the outsiders' view of it didn't keep up - so now, most people outside the field assume that "being in IT" is all one and the same no matter what you do in it. When in reality, "being in IT" is about as vague as saying "being in health care" - anything from an orderly, to medical receptionists, to doctors, nurses and dentists.
All the companies I've worked with were quite tech-savvy, and the product was either software or high-end technological hardware. So when we say "IT", it just means the internal support crew and network administrators. The whole idea of conflating "IT" to mean the software engineers would be just as culturally absurd as calling hospital support staff "doctors".
I would assume it's the same in most software companies (or other tech savvy companies). "IT" would mean the internal IT support people, and anyone who actually writes the software would never be labelled "IT", but rather correctly referred to as engineer, developer, programmer, or whatever.