You need to relax. Where's your Christmas spirit?
First of all, count yourself as one of the lucky ones that were actually able to find an iPod this Christmas, as Apple is effectively sold out!
Secondly, you should always do your research when buying a (relatively) expensive item like this, especially when the purchased item deals with technology! It doesn't take much time and effort, and is worth it in the long run, as you have just proved yourself!
Thirdly, don't be mad at Apple or Jobs, and for that matter, don't be mad at the salesperson either, as anger never solves anything. What does being angry accomplish in this situation? Absolutely nothing. I always laugh and shake my head when I see people waste so much time and negative energy on the most trivial things. The salesperson is to blame here, however he is probably working for minimum wage and has been working off his feet during this whole Christmas season, and maybe has lapses from time to time. Possibly, he is simply not that bright. The salesperson is human, and we all make mistakes. Have you never, ever forgotten to tell someone something? Have you ever made a mistake?
Lastly, sometimes these little details are not mentioned by salespeople, whether that's right or wrong - the example that comes to mind that happens all the time is with regard to printers. You buy a printer, but you do not receive a USB cable to attach it to your computer. Sometimes salespeople tell you this, other times, they do not.
In conclusion, you're overreacting. The iPod is an excellent gift, and it would be very unfortunate if you let this minor detail ruin your thoughtful gift, or put a downer on Christmas. These things happen, so it all comes down to how you deal with it and what attitude you choose to have - it's your decision on how you want to react to little setbacks like this. Personally for me, I have more important things to spend my energy on, in positive ways, rather than expending negative energy regarding a simple little USB cable. Put things in perspective and you'll see that this isn't a big deal at all.
So go out, buy a USB cable for your nephew and let him enjoy his gift from his thoughtful uncle, rather than complaining about it - and have a Merry Christmas!
