Yes - the CVT is definitely a contributor to relaxed motorway cruising. On the flat, at 70 mph, you are doing 2,500 rpm (ish) whereas in a manual car of most other makes you'd be doing 3,500.
If I did a lot of motorway driving - rep type mileage of 100 miles plus a day - I'd want something bigger and more powerful with a less stressed engine and more metal round me.
But, for a small car, the Jazz is a competent motorway cruiser - and that applies to all marques.