There's usually more than one way to skin a cat (and obtain ebooks). Purchasing's one, as previous posters have already discussed; borrowing's another.
AFAIK, online access to public libraries (at least in the USA) is possible worldwide. Searching
Worldcat.org will quickly reveal whether or not one's library carries a given ebook. (Some of us MobileReaders patronize multiple libraries.) Moreover, some digital bookstores (e.g., Kindle's and NOOK's) offer "lend me" options.
Therefore, if I were traveling out of state or abroad, had Internet access, and wanted to obtain a book I couldn't or didn't want to purchase while traveling, I'd try to borrow it. If I were unable to borrow the book, I'd add it to my "To read" list and then download a free sample from the NOOK Store, as a reminder to snag the book when I returned home.