The difference is that in the new design there is a lot more time to make that merge. The issue with the standard cloverleaf design (and why it is no longer used) is because you have traffic trying to merge on and off the interstate in a very short stretch of road. At this intersection today you have about 600 feet of space to merge. If you're going the speed limit, it takes about 6 seconds to drive from one end of the merging area to the other. You're realistically not going to merge in there right at the far end of the merging area, so really you only have 3-4 seconds. If traffic is busy at all, there are going to be 2-3 cars in there at least so now you have to find a gap and get into it all in that short time. Meanwhile you have to judge the speed of the other cars and speed up or slow down as appropriate. The cars coming in are driving in a curved path so it's really hard to judge their speed. And if there's a semi or two in there, forget about it. You have almost no opportunity to do the merge.
In the new design, you have a few thousand feet to merge with people who are going the same direction and same general speed as you. You have way more time and it's a much easier task.
When you do traffic design you are not designing the highway for the optimum driver, or even the top third. You could design the bare minimum space needed to merge and assume perfect meshing for traffic and it would work if only the best professional drivers were allowed on the road. Realistically, you have to design to make things easy because people aren't perfect and you can't expect them to be 100% tuned in 100% of the time.
Exhibit A:
http://www.kcci.com/article/caught-on-video-semi-pushes-teen-s-car-down-interstate-35/6922810