You are right. Henry Ford was known to be thrifty but he definitely was not cheap, nor was the Model T. Inexpensive, yes; cheap, no. Having worked on many of these cars over the years, I have been repeatedly amazed by how well engineered they were and by the continious quality improvement program that was in place at Ford. While they rarely threw out older parts, literally nothing from a 1909 would have been a correct replacement for a '26-7, and visa versa.
When teaching a student driver about the car, I tell them you have to look at the car in context. When it was introduced in 1908 (as a 1909 model year car), the Model T was the iPhone of its time. To that date it was the single most important, and successful, commercial product ever. It got that way because it was affordable and of tremendous quality, not because it was junk. They endure for that reason as well as an intangible factor...they are a hoot to drive.