I call this the "degrees of separation" rule. How far is your job from the point where the company makes money. Sales and accounts receivable (as much as we like to make fun of them) are pretty high on the totem pole. After you get past the politics, they tend to enjoy some form of stability. And it's not uncommon to hear of a salesman/woman work 10 years in the same company.
On the other hand if your job is writing software for a widget company than it better be vital part of every widget. You don't want to be the guy that is made redundant because what they assumed was good work contributed nothing to the overall business.
Or what if the good work you did contributed quite positively to the business, but in a way that wasn't directly connected via the dots back to you. For instance, what if you write a kick-ass piece of software that doubles the sales team's efficiency, but no manager ever gets farther than congratulating the sales team on a miraculous performance because the believe nothing behind the scenes changed. What if they continue to believe this, in spite of your appeals that it was your software that helped the sales force along?
A company managed this way is a company that will have little left but a sales and marketing force eventually, because the executive staff will have pruned everyone else as being redundant. Arguably, this could happen even in a shrinkwrapped software company, where the software isn't just a vital part of the business, it is the only part.
Hire someone incompetent, or see someone incompetent get hired above you, you may find you'll be made "redundant" even if you are the last developer hacking on the product. It is employment at the will of your employer, and nothing says they can't terminate you due to their own incompetence.
On the other hand if your job is writing software for a widget company than it better be vital part of every widget. You don't want to be the guy that is made redundant because what they assumed was good work contributed nothing to the overall business.