> basically no numbers in real world programs weren't constrained, it was often tests, toy programs

The fact that C and C++ compilers generally chose to leave int at 32 bit on 64 bit platforms, combined with the standards requiring "usual promotions" for smaller types to go to int bites me all the time. I'm very happy that Rust dodges the promotions problem altogether, and I'm sorry if I'm wrong about the array subscripting thing (does the snippet I provided panic at 1<<32 or 1<<34?).

> And not everybody is running on 64-bit hardware, so it's a broader default.

That argument could be used to justify 8 or 16 bit integers... :-)