For me, that's quite understandable, and the choices are no brainers.
Sex vs the net. I won't go as far as to say I'd curl up and die without the net, there's seldom a day goes by that I don't use it, even if it's just to hop on and look up a comic. Sex on the other hand is grossly over rated. It's often "marketed" as the best thing ever, when in my experience it's usually just "meh". As for putting my money where my mouth is, it's been over two years since I've has sex with a partner, and a month since I've had to take things into my own hands. Do I think about it, yes. Do I want it, from time to time. But I can do without.
Booze vs the net. Well I've already weighed in on the net. Drinking is another activity I find over rated. Like hot drinks, it's not something I really aquired a taste for. Except for zombies and kamikazes, but they're sweet tasting. Mom never touched the stuff. Dad would enjoy a beer after work in the summer, and overindulge a couple of times in the year. So it was never a big thing in my upbringing. Being an introvert, kept busy, and under tight scrutiny, I never went out and partied in high school. I did have a few goes of getting drunk in university, but in the end I decided it wasn't worth the cost. (Where alcohol is involved, I'm a featherweight) The last drink I has was about seven years ago, and let's just say I thought it was a horrible waste of a Coke. Of course, also being on anti-Ds now, and alcohol is counter indicated, just makes it a wise choice.
So yeah, I can see where others would be willing to pass those up.