It is true that if you've paid for a game you should be able to do what you want with it. As long as it's legal, and does not conflict with the End User License Agreement. A single copy of a game can be traded. But, please, lets differentiate between 'trading' and re-selling. Anyone is allowed to trade their games.
But, like Chris said above, that does not mean copying it and selling it illegally. That does damage the indie scene. Trading a game is another matter. Some people seem to have an allergic reaction to online ordering, so rely on trade to acquire new games. There's nothing wrong with that, as long as the person trading has not copied the disk.
With no control over where game units are going there is a further risk of increased piracy. Some may be surprised to learn how easy it is to pinpoint pirates. If a pirate game appears within the first week of official sales it does not take long to check the records and locate the culprit, and then take immediate action.
Furthermore, I find it upsetting when certain individuals order more than one copy of an indie game, stating that one was for friends or family, only to see it on Ebay on the day of arrival, knowing full well the game is rare (in comparison to a mainstream release). That's dishonest, but there's little you can do about it. It would not be the first time that individuals have attempted to profiteer from others hard work.
I'm glad that adventure games still appear in stores in the US, but it certainly is not the case in the UK. More often than not adventure games have to be ordered online, and shipped.
The PC section of all game stores is shrinking fast, so the days of buying PC games (in stores) are numbered. Add to this the small fact that large publishers 'reserve' shelf space for titles. If they do not have a title to release, the space is rented to another publisher for big bucks. The position on the shelf (in terms of head height) and number of units is reflected in the price of the rental.
The future of game distribution is online. Whether this happens quickly, or slowly, is another matter.
As with any venture, there are highlights and pitfalls. Creating and publishing a full game is one of the most intimidating projects you can imagine, especially for an individual. Unlike many of the copy'n'paste games produced by the larger development studios, an indie effort is always a personal project, with time, personal finance and passion invested from the very start. The game sells in, relatively, tiny numbers in comparison to the mainstream. It's easy to keep track on who has copies, and who does not. That, I feel, is why it's upsetting that a few of those orders were made purely to re-sell with absolutely no benefits to the developer, or their future games.
Lastly, thanks to Manxman for a lively topical topic. It's nice to see some bristling text here and there. It shows that interest and opinion is as strong as ever. It is a forum after all.
On a positive note, which I always prefer to end on, I will say that it's wonderful to see more indie games appearing year by year. The opportunity to sell indie games online has become a mini-industry in itself, and means we (as gamers) are able to choose from a delightfully diverse range of games, styles and subject matter. The indie scene is delicate, but it is supported, and can only thrive as more and more gamers become accustomed to online ordering.
The ghosts are waiting, in the dark places, the forgotten places. Waiting for you: Darkling Room Games