Within SA almost all LAN (and family) flights are on A319-class a/c with 'domestic' biz seating. There are two similar-but-different "visit South America" ticketing schemes that imo offer reasonably-priced coach seating. One is LAN's own scheme, the other is OneWorld's. The "Oneworld Visit South America air pass" requires that you buy at least 3 segments (before arriving in SA on a OneWorld airline, and leaving on one), and no more than 16 due to e-ticket restrictions. They book into B or K, give full miles and q-points for AA, don't know about others, and are fully flexible, including add/drop segments - USD25/50 change fee. They're priced in mileage brackets:
Zone 1: 0 to 560 USD119
Zone 2: 561 to 750 USD143
Zone 3: 751 to 1280 USD179
Zone 4: 1281 to 1810 USD203
Zone 5: 1811 to 2300 USD263
Zone 6: 2301 to 3500 USD359
(Data from a 2008 table, but seemed very close in late 2012)
OW ticketing was arranged by speaking with the AA RTW desk, but of course online arrangements may now be possible. LAN's can be ticketed on-line, but their sites can be 'difficult'.

I didn't intend my original post to be denigrating in any way, btw. I just can't imagine going off on my first rtw (in my case at a relatively tender age, and mostly on B707 aircraft) without first having spent a lot of time curled up reading the personal stories of those who'd already done the trek.

The nexus of year-travelers used to be KTH and Goa, btw. Goa seems all touristy now, haven't been back to KTH recently enough to comment but if politics hasn't destroyed the place the gang might still gravitate there. I envy you all, having never found more than a couple of months for the trip. Bucket-list item, perhaps.

And now that I've joined the advisors, against my own advice, I can't resist mentioning that a long RTW should not miss Kruger National Park in South Africa. Very inexpensive DIY wild-animal experience, not counting the cost of getting to JNB. At the expensive end of adventure travel, a visit to Antarctica on an expedition-class ship (e.g. MV Ushuaia) easily trumps anything else I'll admit to.