Well of
COURSE it's difficult/tough! It's no different than anything else worth having/doing. i.e. the person who has a clothes/shoe fettish and $10,000 in credit card debt they can't pay off...walking past a store in the mall. Or better yet, not going to the mall in the first place.
You're take, quite frankly (no offense) is such a cop-out. An excuse. Giving your/her power away. If your wife
really wanted to lose the weight, more than she wants to feed her face, she'd do it. And not because 99% of the rest of the planet wouldn't love to feed their face if there were no financial, health/fitness, or "appearance" consequences. Rather, because others have decided that looking good and/or staying healthy is more important than those few seconds of pleasure that their taste buds send to their brain.
Until she gets serious and walks even 5-10% of the talk, it's all noise. Kinda like a meth addict saying they're gonna go clean, then surrounding themselves with dealers and druggies without any change in personal habits whatsoever. Your wife may think she wants to lose the weight, but she doesn't. She just wants to have her cake (eating more than she should, eating the wrong foods, not exercising enough, et al) and eat it too. But if she really, REALLY gets serious about dropping those pounds, she'll let other people eat that cake...and eventually never even buy it in the first place.
While I absolutely agree that it takes will and discipline,
losing weight is not simply an issue of willpower.
Sorry to be standoffish...but yes, yes it is all-about willpower. The power to look at that piece of pie/cake and say "no thanks." The power to buy more fruits, vegetables, and grains at the grocery store, versus whatever sugar/cheese/chocolate flavored snack happens to be staring at you from five feet away inside a colorful package with a "toy inside."

The power to make yourself a healthy dinner instead of rolling into a fast food joint to get your 1,500+ calories of ___________. For a very-few people, there are issues outside of their control (i.e. the thyroid condition someone mentioned earlier, or a lengthy bout of being laid-up after an injury, etc.). That said, as an adult, there is only one person who controls what food and beverages I put inside my mouth, and how much of said food/beverages I consume:
ME. And unless you're telling me these people are chained down to a table (unable to exercise) and are being force-fed sweets, fatty foods, et al through a tube, there is only one person who is responsible for the fact that said individuals cannot consume less calories and/or eat more healthy foods: the people who ##### about being too heavy.
I'm not free from the finger pointing here either! Like I said, when I was on those meds for a while, my weight ballooned up from 185 to ~214! But ultimately, the ONLY thing that got me on the right path and helped me drop all those excess pounds was to stop playing the blame-game or "poor me" card and:
1. Admit that my lack of willpower and self-control was causing me to eat too much food, or the wrong kinds of food, and
2. Exercise through the pain. Exercise is going to hurt. Particularly the more out of shape one is. But if I didn't push through that pain, I was going to be a fat-### until the day I died.
So until anyone who is having a pity-party about their weight and not looking good can look themselves in the mirror and say
"I am to blame for letting it come to this...and only I can take responsibility/control to change myself for the better," it'll always be 2-3 steps forward, 1-2 steps back. Sounds harsh, but it's meant as tough love.