Well both /ame and /amsg pre-date while loop support in mIRC scripting so it's not really much of a comparison. Plus there's a typing convenience factor for using those commands since they're expected to be used by a regular user rather than a scripter, whereas the /echo command is used primarily in scripts (after all, why would someone chatting use /echo from the editbox?).
Maybe it'll be added, maybe it won't. I'm just saying the existence of /amsg and /ame doesn't have any bearing on whether there should be a similar ability for /echo.
