Comment by thayne
But in that case, once the fermentation system is built, the brewery no longer needs that employee.
A better analogy is a brewery hires someone who builds a fermentation system, then continues to operate, maintain, repair, and improve the system over time. Some of the employee's time is spent on work that could probably considered R&D, some of it is on work that is clearly operation, and some isn't clearly one or the other. So how do you determine how much of the worker's salary is R&D vs operational expense? You can try and estimate some percentage, but that breakdown is at best an educated guess, and having to try and figure that out just adds pointless friction.
But that still isn't a great analogy, because in that case the fermentation system isn't the product, the beer is. So for a company that sells software, it would be more like if it wasn't a company that sold brew, but a company that rented out or sold its brewing equipment to other companies that made beer.
Also, the same argument about creating value that pays off over time could be said about most employees. An accountant could find a more efficient way to keep the books that pays off over years; the CEO could create a strategy that pays off over years; customer service staff could create a reputation for high quality customer service that pays off over years; etc.
And then, even if you assume that an engineer's salary is entirely R&D, then the only reason I can see to want that salary taxed at a higher rate is if you want to disincentivize R&D. R&D is already a large expense now in the hopes of a payoff later, and by increasing the tax burden now, you are making that upfront cost even higher.
How about actors? They produce a thing (content) that is sold for a prolonged period of time. Copyright is what, 20 years?
How would Disney feel if the salary paid to the cast of the Avengers was no longer an expense in that year, but amortized over the entire copyright period of the film.