Because we can store enough things to fill memory?

Name me a particular time where a file format has ever had increased robustness, speed, security, or implementation simplicity because it did not specify record size ahead of time.

Please convince me of the reliability of sentinel values and null-terminated strings.

Apologies, I didn't read the spec before hand. I thought you were suggesting that the format have fixed sized fields rather then fields with tagged lengths. In that case I'd agree with you.

No sweat. :)