From Leupold's website, the description of the VX-3i: (bold black done by me for emphasis, and red bold text added by me)
Versatile magnification ranges and an attractive new look make the Leupold VX-3i riflescopes ideal for virtually any hunting situation. The aggressively redesigned power selector is easy to grasp and turn and allows the shooter to quickly verify the power setting even with gloved hands. I can't say that I see anything that "aggressively different" than before, at least not in the single image they offer of the scope The Xtended Twilight Max lens system delivers the highest average light transmission in all colors for exceptional contrast and low light performance in all conditions. Edge blackened lenses reduce diffusion and glare to improve resolution and contrast. Second generation Argon/Krypton gas more effectively resists thermal shock and the dual spring precision adjustment system ensures match grade repeatability and strength. well now ... I guess these are more than ok for competition level benchrest scopes Top it all off with DiamondCoat 2™ external lens coatings for scratch resistance and you can see why the VX-3i is the first, last, and only name in riflescopes. As always, each Leupold Gold Ring riflescope is factory tested to be the ultimate in ruggedness, reliability and absolute waterproof integrity. Covered by the Leupold Full Lifetime Guarantee.
On a more serious note, I agree with the post above ... they appear roughly the same as the older VX-3 line ... the internals may be re-engineered or just beefed up, I don't know. As time goes by, we can always expect gas fillings to be improved, as well as lens coatings, so that's no big deal there.
I'm really wondering if these are practically the same thing as the VX-6 line, but w/out the internal magnification system that allows a really huge range (ie: 3.50-10x vs. 2-12x). I mention that only because I'm trying to figure out what makes the VX-6 so appealing vs. the VX-3i, unless you simply MUST have a scope w/ a huge magnification range.