The thread that you heard it from was a weird thread.
The OP of that thread was referring how because the iPhone 3G's spec showed 163 ppi while the iPod Touch's specs was also 163 ppi, the iPhone 3G is worse than the original iPhone (because the iPod Touch's screen was deemed worse than the iPhone's screen)
First of all, 163 < 160 doesn't even make sense.
Second of all, just because the numbers match, doesn't mean the screen is the same (1.8 Ghz AMD != 1.8 Ghz Intel).
Third, the first iPhone's ppi was most likely rounded down.
Lastly, refer to the second point.