[mprime1]

Rounding up 'usually works' to 'is reliable' is a recipe for building crappy systems.

Rounding down 'usually works' to 'it's not perfect and we need to handle edge cases' is how you build dependable systems.

Your first comment seemed very much in the first camp to me.

[acdha]

Your second camp is the latter half of my first sentence. As a simple example, the transport layer cannot prevent a successfully-received message from being dropped by an overloaded or malfunctioning server, duplicate transmissions due to client errors, etc. so most applications have mechanisms to indicate status beyond simple receipt, timeouts to handle a wide range of errors only some of which involve the transport layer, and so forth. Once you have that, most applications can tolerate the slight increase in TCP failures which a different protocol would prevent.