What you read about the roof in 529 is there as an example. So you're absolutely correct in "same logic applies". It gets weird when dealing with a comparatively low cost expense such as replacing a hot water heater. The hot water heater is "in fact" a physical part of the plumbing system, which is a physical part of the rental property. Depreciating an $800 water heater (that price includes labor for installation) over 27.5 years will result in absolutely no tax benefit what-so-ever. Thankfully, the di-minimus safe harbor act would allow you to just expense it, and claim/deduct it as such in the tax year the expense was incurred.
