I don't want to be the devil's advocate here, but doesn't a short lifespan work in HER favor if she doesn't really want an EM?
I'm not sure where she's getting her "EMs aren't smart" thing. If she's refering to the intelligence tests I think she is, itworks on things like command obedience per time spent teaching it (IIRC, correct me if i'm wrong) which is pretty skewed. Sure, a Border Collie might answer "Come!" right away and after only 5 repetitions, but if there's a car coming i'd rather have the mastiff that thinks about it before leaping into the road. My friends have a Black Lab and although Labs score higher on "intelligence", that dog would hold the door open for a robber trying to get into the house while my Ebony would raise a ruckus and most likely back him down on sheer intimidation.
I also can't stand yappy dogs (all the big dogs I've been around, volunteering at shelters, etc. and I've only ever been bitten my tiny dogs with Napoleon complexes), so I hope you're able to convince your wife!
~Marrow
EDIT:
Okay, found what I was looking for:
http://en.wikipedia.org/wiki/The_Intelligence_of_Dogs
It's a popular "intelligence" study, but to quote the article (emphasis mine):
"The drawback of this rating scale, by the author's own admission, is that it is heavily weighted towards obedience related behavioural traits (e.g. working or guard dogs), rather than understanding or creativity (e.g. hunting dogs). As a result,
some breeds may appear lower on the list due to their stubborn or independent nature, but this nature does not make them unintelligent or impossible to train. The book includes other sections on hunting and other intelligence types, as well a general IQ test that owners can perform on their dogs; that test is better weighted for ingenuity and independent problem solving, but rankings were provided only for working intelligence, and are listed below."
With this test, "Mastiff" ranks at 72 and "Bullmastiff" at 69 (out of 80). I think the bolded phrase above just about sums it up. Mastiffs are not stupid, they're bred to protect and guard and as such have to independently assess threats and
choose how to act. It would be ridiculous if they waited for "permission" to sound an alarm, or wouldn't bite an attacker unless commanded to do so. Ebony sometimes refuses to obey a command, but it's not because she doesn't "get it", it's because she doesn't see the point in endless repetition.
/End rant