Для wikipedia надо иметь доступ к интернету через wireless (Wi-Fi). Через USB можно только закачивать файлы на Kindle, чтобы потом их читать в оффлайне.
Для доступа к wikipedia есть 2 пути:
3G and wifi are two ways for the kindle to connect to the internet. You don't need an internet connection to read ebooks and newspapers that are already on your device. You need a connection to download new content to your kindle, and also to use kindle's browser to surf the internet. Let's suppose for the moment that you don't use Kindle's browser very often.
If you don't have wifi at home, you should probably get the 3G model, otherwise you'll have to take your kindle to a wifi hotspot every time you want to download a book or newspaper.
If you do have wifi at home, you can probably survive without the 3G version. What about when you're away from home? If you read ebooks while traveling, just load up your kindle with a few ebooks before leaving home. It becomes an issue if you subscribe to a daily periodical on your Kindle, like the New York Times; then, it's handy to have 3G so that you continue to get your new issues every day. Yet, wifi hotspots are popping up everywhere - many of them free - so 3G connectivity is less and less a necessity for many of us. And, 3G coverage is not universal - I have two sets of relatives I see regularly who live in areas where 3G coverage is spotty; but in both of those towns, the hotels I stay in have free wifi, so I'm covered.
If you use Kindle's web browser frequently, it may be worthwhile to get the 3G model. I don't really like Kindle's web browser, and my phone has a good web browser and display, so there's almost never a need for me to use Kindle's browser.
Most of this argues for getting the cheaper wifi version. But there are reasons to consider the 3G version. First, the extra money you pay for the 3G version buys you unlimited lifetime free 3G service; thinking of it this way, the price really doesn't seem unreasonable. Second, the more you're away from home, the more likely you'll find yourself in a situation in which wifi isn't available but 3G coverage is good; probably not TOO often, but once in a while. Then, it's nice to have 3G, especially if you get a daily periodical or if you want to download a new ebook.