To tri bike or not to tri bike

Until I signed up for my first tri (2007), I had not ridden a bike in years.  I trained on an old mountain bike (Trek 400 series) with knobby tires until my marvelous husband bought me an entry-level tri-bike (K2 T9) later that same year before my race.  The moutain bike went to Colorado with my sister that summer and has since been stolen. 

I still have only the tri-bike, and no need for another bike.  It is comfortable for training, toodling around town, towing my kids on the tag-a-long or in the trailer or whatever.  For bigger hills (in the mountains, for example), I might want more easier gears but for now I need more work on my engine instead.  I see absolutely no need to have a road bike. 

Does the biking community say not to train on the tri bike because of the wear and tear on the bike or on you?  If your bike is well-adjusted, you shouldn't experience any additional discomfort on it over a road bike.   Wear and tear on the bike?  Well, maybe that would be an issue if you bought a really really expensive bike, but I call BS.  Even if you did have a $3K+ bike, wouldn't you still want to be very familiar with it and comfy on it so it felt like it was a part of you?