> ...I'll simply start taking days off without pay, which is something payroll seems to really hate for some reason when it concerns salaried folks.
At the risk of sounding too glib, the short answer to why they hate it is it creates work for them. In the US, all of the major payroll processing services are geared towards either hourly or salaried templates. Most companies' payroll procedures are built around the core assumption that if you are salaried, then it is X salary divided across N weeks/months/your-pay-period. If you take days off without pay, changing the salary, someone in payroll has to manually key in the delta off your normal pay period processing numbers. That sometimes has downstream ramifications upon unemployment insurance reporting and remittance, for larger companies there are other regulatory-originated reporting that this can impact, and put in common issues like tax liens and family court-mandated levies, just for starters, and it gets hairy. Generally payroll processing is still built around a set of assumptions that are at odds with emerging knowledge workforce trends; the trends can be accommodated, but it's a hassle.
If you have a good enough relationship with your manager, then you are far better off negotiating a sub-rosa agreement to (in your example) work Wednesday this week and take off a couple days next week (or leave a couple hours earlier each day), and net out to zero change in time worked over a short (sub-month) period and leaving payroll none the wiser to any change in time worked, than making the payroll department perform an exception-based processing of your payroll.
US payroll processing trivia to illustrate how rigid payroll processing systems are today for the small business, and for flexible work arrangements: if you are a really small, micro-sized business, like say an Etsy seller with a couple full-time employees, set up as your own LLC or whatever, you will run payroll, except unlike larger businesses you will frequently want to know how much to pay yourself (after paying off all employees and vendors) including all employER-side tax liabilities, and not just the employEE-side disbursement. All of the top-ten payroll processors have no capability to compute that for you; you have to iterate to an approximation. In other words, if you know you can afford to pay yourself only $10K total this month, payroll processors force you to key in a employEE net pay number then they spit out the gross including the employER side, and only then do you see if you are over/under the $10K amount. There is no feature that lets a small business owner say, this pay period, I can only afford at most $X cash out the door total including all tax liabilities for so-and-so employee, iterate and solve for me what the best result is to achieve that.
US payroll processing can get really complex, really fast even for small businesses, so I can imagine what a nightmare it must be for the designers and developers of those systems. However, I believe there is still plenty of room for someone to create a disruptive service that caters to and appeals to small businesses.