Wow! I can't decide if you're brave or suicidal posting that on here. On reflection I think brave. I haven't read all the responses but got the gist of mood so for what it's worth here's my take on it...
No your wife is not a bad Mother (at least I'm assuming not). If you have any major concerns you should be speaking to your GP/Health Visitor/Social Care. Since I'm assuming that's not the case I wouldn't worry. How are the children doing generally? Do you think they're developing roughly in line with their peers? (Be careful about comparing too stringently as every child develops differently.)
Is your wife normally 'jolly and outgoing' or however you described it or is she usually quite reserved. The same for you really? My daughter seems to be taking after her Dad (loud and outgoing) whereas my son is more reserved like me. When we used to go to baby groups he'd be the one either crying or lying there ignoring everyone. I take my daughter now and she's smiling at everyone and interested in everything. I think generally speaking personalities are what they are and although nurturing has a role to play it's nature that wins out on this one.
My final point is that I know I'm guilty (especially when my husband is there) of switching off a bit. My reasoning (although that sounds a bit coldly logistical) is that I spend pretty much 24/7 with the kids. I interact with them, I do this while cooking, cleaning, dog-sitting, visiting etc. I don't get to sit and watch tv for hours on end (or even minutes on end), every time I meet up with friends my conversations are constantly interrupted (by mine as well as their children). I also find that I switch off a bit when it's just me and them. Not in a neglectful way but just if I'm busy changing one nappy the other child has to wait.
So what I tend to find is that if my husband or a grandparent is there I enjoy taking a bit of a backseat. I'm also not somebody who tends to chat and chat and pull faces etc at my little one when we're in public. I would imagine your wife does the same. If she's constantly juggling life with three kids why shouldn't she relax a bit when you're around? I think I also read that you say you work away quite a bit so that must make it even harder for her.
So overall I think I can understand your concerns but I think they're unfounded. Please don't let your wife know what you're thinking. I bet she's got enough on and doesn't need to feel undervalued. As long as your kids are happy and healthy you're both doing a great job.