Anyone who sizes the fuse to be exactly the same as the expected draw of the device has literally designed in a problem.
As Alti explained, clearly in the US. of A, yes, which I was not aware of!
As per IEC standards, one can design a fuse to carry nominal rated current indefinitely - no problem.
This is just an arbitrary choice someone has made. Both ways of thinking are valid, but the USA way would require the fuse manufacturer to separately specify the current which
can be used (equivalent to the European In, just under different name), and as the Bourns example shows, they don't always bother doing that (and then you need to assume some "derating" factor)! With our European fuses, this is simply the rated current, so one number less to specify.
Note this has nothing to do with fuse construction itself, curve shape or anything like that. Just a maybe ~25% discrepancy in nominal rating.
What to call "nominal" is always a tad problematic. For example, tantalum capacitor manufacturers define nominal voltage as something which will destroy the product in short time, so that significant derating is always needed, while aluminum electrolytic capacitor manufacturers chose nominal voltage as something that the part can be exposed to indefinitely.