And do you believe this is seriously something that is killing companies left and right?
You know what kills companies? Cashflow.
So if you're barely staying alive, anything that doesn't soon lead to revenue and acceptable gross profit is a luxury you can't afford.
On the other hand, if you are an owner with a steady profit-generating machine you want to keep it running as smoothly as possible as long as possible. Investing a relatively small amount directly in your employees' professional development is a way to help this happen.
Employees like to stay current and feel like you care enough to keep them current. Going from spending $0/yr on someone for training to $1000/yr will probably make them a lot happier than a $1000/yr raise. That might be as simple as giving a group a collective budget for books and courses on anything related to your business.
There is a definite cost when a core member of your team, no matter which level, moves on due to boredom. This is one way to keep them a little happier. Some aspects will show up in your company's resources beyond just happier employees too.
That, in turn, gets (eventually) impacted by innovation debt.
> And do you believe this is seriously something that is killing companies left and right?
No, not at all; and I don't believe the author of the post does either. There is a whole bunch of things that can kill a company (especially a startup), and a lot of them are going to be bigger and more urgent then innovation dept. You should definitely focus on dealing with those. However, innovation dept should not be dismissed entirely, especially since it doesn't take much to offset it.
But like you said if you have little to no cashflow right now then that is going to kill the business faster. It's all about finding a balance. You need to make sure that you have the cashflow to get to the point where having a sustainable code base and talent matters. If you worry too much about innovation debt off the bat you'll never get out the front door, but if you don't worry about it at all you will likely reach a point where everything eventually comes crashing down.