Some of you may have noticed the Myst series added to Steam's catalogue on 4th-5th Aug:
realMYST ($5.99)
Riven: The Sequel to MYST ($5.99)
URU: Complete Chronicles ($9.99)
(Prices above are non-discounted, in USD.)
The prices are the same as on GOG.com. realMyst and Riven currently have a $1 discount.
Steam's Cyan Complete Pack ($19.99) (2 USD saving) includes the above 3 plus, for free:
Cosmic Osmo and the Worlds Beyond the Mackerel (not on GOG)
The Manhole ($5.99 on GOG)
Spelunx and the Caves of Mr. Seudo (not on GOG)
Considering the price point for having all three is the same, GOG.com should look into getting the same deal - if you have or buy all 3 paid games, you get the three free games (or some better deal).
Ofcourse, I'll be getting the DRM-free GOG version of all 3 even if it's 2 USD more.

I'll finally purchase it from GOG if this happens!

Are you sure you're not getting confused with the Journeyman Project 3? The DVD version of that had higher resolution graphics but I wasn't aware of a difference with Riven.
EDIT: Wikipedia mentions better audio but that's it.

Couple links where people talk about the differences:
http://www.dpwr.net/forums/index.php?s=af23007df04ed455d32c39d77a433b3e&showtopic=816&pid=7331&mode=threaded&start=#entry7331
http://www.gog.com/en/forum/myst_series/riven_graphics_cd_dvd_comparison

Ah cool. +1 on wanting the DVD version then. I've owned the CD version for years but if GoG gets the DVD version I might buy it here too.
Having said that, you said higher resolution. No one else has said anything of the sort... But I'd welcome less compressed videos.