No, this is silly.
Check it;
http://www.ultimate-guitar.com/tabs/...guitar_pro.htm
DT seem to get a lot of shtick purely because, at least as far as I can tell, they are popular-ish. And prog isn't allowed to be popular-ish.
Not only does this song have the time signatures, but also the more subtle things - the scale changes, constant chord changes, style changes (ragtime solo). Also, it is "progressive" in the literal sense of the word - it doesn't go verse-chorus-verse etc, it's evolves and changes throughout the entire song.
For me, sometimes it can be hard/impossible to say what is prog and what is not. To me, prog seems more like a quality of the music rather than a particular style. Any genre can "be prog"... it gets confusing. Sometimes I wonder wether we should really call stuff "prog" or instead, just call, for example, Rush would be heavy rock that is pretty proggy, and Dream Theater would be metal that is proggy, etc. Jethro Tull would be Folk Rock that is proggy etc.
But Dream Theater are definitely pretty damn proggy. Sure, there is proggier out there, but there always is.