Everyone's definitions of "mecha" here seem rather, um...personalized.
Mecha are machines, plain and simple. Macross is mecha, Star Wars is mecha, Transformers are mecha. Eva, IMHO, scrapes by on the fact that they don't reveal that the Evas are completely organic until near the end of the series.
http://ja.wikipedia.org/wiki/メカ
Also cf. the Studio Nue Mecha Design Entertainment Bible, which contain space ships, drivable robots, androids, bases...pretty much anything mechanical.