You're funny.
You think cutting your hours is paying for his fancy vacation.
Yeah, I don't think you are making that kind of money. Having you work 4 hours a day instead of 8 is probably not even paying for dinner on vacation.
I guess the owner doesn't care if the website is updated nor that people aren't getting coupons. Or maybe he has figured out another way, besides you, to get this stuff done.
Life isn't fair, he may have any number of reasons to cut only your hours, those soccer moms with other income might quit if he cuts them or their kids may be friends. He either doesn't think you will quit or wants you to quit or you are over paid for what you do.
He's cutting your hours because you suck. That's how it works. The better workers get better hours.
To you, it is, to him, it isn't. If business is slow, he has to cut spending somewhere. As this is unsatisfactory to you, the only thing you can do is to look for another job.
what you may consider as fair or not, the boss is not concerned with ; you have the option of finding employment elsewhere
If you are the best worker then it is unfair. If you are not then it is fair.