True, but the reality is that clothing as a technology has evolved over a long history, and some types of clothing are more likely to provide the "right fit" than others, particular for folks non-ideal body forms.
If you're in good shape, you can find t-shirts and jeans that look pretty good, but even that isn't easy. If you're out of shape, it's nearly impossible. Conversely, oxford shirts, sports jackets and trousers have about 100 years of evolution in providing a good fit for all kinds of men's body shapes, and they're also far more amenable to alteration by a tailor (does anyone actually tailor their t-shirt?)
If you're in good shape, you can find t-shirts and jeans that look pretty good, but even that isn't easy. If you're out of shape, it's nearly impossible. Conversely, oxford shirts, sports jackets and trousers have about 100 years of evolution in providing a good fit for all kinds of men's body shapes, and they're also far more amenable to alteration by a tailor (does anyone actually tailor their t-shirt?)