More often than not you would just use an existing product if you are not going to add any value.
This is a situation where building a new applications with handmade layers that produce the outcome you want is more efficient than gluing together existing code.
You're coming at a complex problem by initially filtering the solution space. This discards much of the potential solution space for which the average case may be more expensive than The average case in the space after culling. However in many situations that solution space has many gems which are more efficient. Companies' tolerance to selecting those rather than using existing technology varies.
But I get the example about roman numerals, editors and browsers.
I would consider it a browser that used an engine. Now a days everyone but firefox is using WebKit.. not much of a difference.
Curious how you would do that today without vb.net
If it's a complicated problem that can be boiled down to a simple API, I'll reach for it for sure. But I never have good luck with complicated problems wrapped in a complicated API. Usually I only need to solve 5% of the problem, so I'll either find a library that focuses on that 5%, or I'll code it myself.