Well, I have to chime in on this, because I've been on the other end of the addiction.
Having said that, I do not know how much time you spend on Xbox. (I personally, love my Xbox Kinect for exercising. :) ) So I am not going to comment on that, other than it's something you need to really think about and be honest with yourself about.
My partner (previously fiance as we split up over the summer and are now back together and working on our relationship) is a TV addict. He may not classify himself so, but it was the primary thing (other two were smoking and not exercising when he has chronic fatigue and a poor immune system) that made me extremely unhappy in our relationship. He might not have seen it that way, but TV was more important to him than I was (I felt), it was like "the other woman". Our home life revolved around the TV. The TV was almost always on. When he came home from work, first thing he'd do is turn the TV on. On weekends? Unless we went out, the TV would be on all or most of the day. The kids there? The TV would still be on all day.
It was how he "relaxed" and despite the fact that it was a stressor for me, I did not have an issue with that. It was the amount, the way it took over our lives, the way everything revolved around the damn TV. Finish watching a movie? Turn on the TV. As the woman, ARRRRRRRRRRRRRRRGHHHHHHHHHH!!!!!!!!!!!!!!!
Seriously, I felt like I wasn't much different than the living room lamp. I wanted him to pay attention to ME. To feel like I could count on that as much as I could count on the fact he was going to watch TV. Whether or not he'd turn it off, whether or not he'd get off the couch--was the day going to be good or bad (ie an all-tv day)--I never knew.
Don't even get me started on the effect of that on the kids.
Which is another thing: My stepkids. Think it's not possible or an exaggeration to say TV and video game addiction doesn't exist? You would be wrong. Because of their mother (my partner didn't live with them, and because of me, we were the ones who would make them do something else, and was that ever an uphill battle) these kids watch TV and play video games 24/7--or as close as they can get and still sleep. They even do it in order to FALL asleep, they will watch a movie until they conk out at their mom's.
Because of this, they have poor social skills and do not know how to have friends (except 1 who was blessed with a very easy going disposition), they fight constantly because they do not know how to interact with one another when the TV and video games are off, NONE of them knew how to play, and never learned. They developed none of the creativity and ability to entertain themselves that other kids have. They couldn't sit down with toys and play, they would be bored because they didn't know what to do. They are all, and have been since they were very young, obese.
The mother tells the youngest girl, that my daughter is a "stick" because she is a healthy weight. Every time this little girl realizes she is fat, she is traumatized. Denial quickly kicks in--one time my partner found an online calculator which put all 3 of the youngest in the 95 percentile of the obese category. She was devastated. Next morning, she was bright and chipper and told us it had all gone away while she slept. Her mother is perpetuating this, and one day she will realize--for good--she is not normal. The 2nd, has severe back problems due to lack of activity and excessive weight--we have watched that poor child cry and cry and cry for hours no matter what we do to help, because HE EXERCISED. The 3rd, well his behavioural problems are so severe I just hope he doesn't end up in jail one day, he certainly will never become a functional adult. He has autism and he FREAKS if you take video games and TV away from him. He is more extreme, but like the others, he has no idea how to cope without the TV and the videogames.
This didn't happen when their parents were together, they were a healthy weight and started out as healthy kids.
Can TV, Xbox, Gamecube, Wii, etc. be addictive and destroy families and lives? Hell yes.
It can overtake relationships (like mine).
It can make kids think the only way to "connect" as a family is to disconnect and put something distracting in the way.
I am not saying this is the case with you, but if she is telling you it is a problem, it is a problem.
I was not an unreasonable shrew when I got frustrated with my partner for spending more time with the tv than with me. Unless you know your partner to be one, take her concerns seriously.
I never made an issue of it unless it was getting so frustrating that despite my attempts to be understanding it was just too much.
Also, it makes him sound really bad, just this isolated piece, but my partner is a very considerate and self sacrificing man. He did many things for me and showed me love in other ways. But this was a huge issue for us (me). He just wasn't very good in this way, in the past. The results were the same though: I wasn't getting my needs met in the relationship.