One of the core principles of economics is the scarcity of resources, which the subject of economics attempts to address. Put in other words, the problem of unlimited wants and limited resources relative to that is perhaps the sole reason economics exists at all. Generalizing, limited resources is the problem, and economics the solution.
On the assumption that this model of problem and solution can be applied to other disciplines (i.e. mathematics, physics, chemistry, etcetera), what are the problems they aim to solve?
If this model does not apply, or isn't the right framework/question in the first place, what are the first, ur-principles underpinning various subjects?
I believe you meant "in contrast with vertical search like Google".
I agree in general with your point about incentives. However, there is also another angle to consider: other companies. Google will have to keep innovating to some extent; if it doesn't, other rival search services may do so threatening Google's market share (although this threat would probably not be very impactful given the number of people used to Google).