I definitely agree that it depends on the spinner. I spin both ways and I love them both. I got pretty proficient on a spindle before I bought my wheel, and I'm really glad I did things in that order...but some people just never feel the spindle love. I was glad to get my drafting skills down before I had to worry about treadling too. But really, there's no right or wrong way to learn.
People always talk about wheels being faster, and they are -- but that doesn't mean that spindles are horrendously slow. If I predraft I can spin about 100 yards in an hour on a spindle...so it's not as though it takes two weeks to spin a skein of yarn. It's just a different process. And as you learn you'll probably find that there are things to like about either method.
That said -- I wouldn't be too nervous about buying a wheel without having used one -- of course it's best to try before you buy, but if you're determined to learn, IMO it's not a deal-breaker. I hadn't spun on a wheel before mine came (well, I did spend about 5 minutes on a Traveller...not very significant) and with the help of the Internet I was able to get up and going pretty quickly.