>If the culture of a company is well known, articulated and understood, there's a self-selection process that happens. A given culture attracts certain kinds of people -- so it becomes self-reenforcing.
That's essentially my point about gravitation, except my assertion that it doesn't scale. After a certain point, it becomes more important to hire the people the company needs, not just the people that want to work there. Below a certain size it is much easier for those to be overlapping sets.
> that doesn't mean there can't be an overarching culture that is shared organisation wide
I think inopinatus is on the right track in terms of breaking "culture" down into different things. There can certainly be certain values and principles of "how things are done" that span the whole company (note: I'm not saying processes either - perhaps 'ethics' is the right word). But that's not enough to make a culture, and trying to force one out of those relatively small commonalities is where things generally fall down.
Again I think the most important thing when it comes to scaling out is having representation in place at various levels and listening to what people at the lower levels actually want, rather than trying to dictate things in a top-down manner. It is very likely that as teams become more specialised, they will have much more individual needs that might not fit with certain aspects of the original culture. There's no reason that the shared culture can't evolve and stay beneficial to everyone - just expect the size of that shared part to shrink if you are doing it right.
The sad fact is that it's much easier to get company culture wrong than it is to get it right. I'm not going to say I have some magical solution to this because I don't, but I do wish you the best of luck with HubSpot - and the same to AirBnB of course. Just because something is an ominous sign doesn't mean anything is predestined.
One thing that I do think is quite important is that the company culture in a small business tends to be the way it is because the management structure is pretty flat, everyone has a set of shared goals and cooperation is easy. That's another thing that doesn't scale. It's very easy to break a company culture with things like poor management structure, skewed employee incentives, etc., which tend to foster a dog-eat-dog culture and company politics that very often do not exist in smaller companies. Personally, were I currently scaling a business to around 800 staff I'd be worrying most about the management structure and trying to create an environment where cultures can grow organically, while ensuring what remains consistent are the shared values, goals and company vision.
I think by focusing too much on the company culture at the top level, it's easy to lose sight of the forest for the trees. In macromanagement there's only so much you can directly control and culture isn't one of those things. That means getting the outcome you want by indirect means, even if it doesn't look exactly how you might have pictured it.