The perception is based on Jaguar scoring very well on Initial Quality, which is a study that records problems in the first three months of ownership. In 2004, Jaguar scored its best ever result -- 98 problems per 100 vehicles, placing it third overall (behind Lexus and Caddy.) The average for the industry was 119.
However, the tell-tale reliability study is VDS (Vehicle Dependability Study,) which charts 3-year reliability.
And in this test....
Jaguar had 310 problems per 100 vehicles, where the average was 269, the best (Lexus) was 162 and the worst was 472 (Land Rover.) Volvo was also extremely poor with 346. Ford brand was right behind the average with 276. The only Ford marque to score above average was Lincoln, and studies do show that Lincoln, Buick and Caddy owners are less likely to report problems, since they tend (on average) to be less aware of the condition of their vehicle. (I've always joked that with an average buyer age of 72 years old, Lincoln's slogan should be "The Last Car You'll Ever Own --- Literally!"
My inlaws have a 2000 S-Type 4.0 and a 2002 Lincoln Navigator. Both have been extremely problematic, and the Jag dealer proved to be worthless. They couldn't reproduce a problem that I could reproduce like clockwork. (It was a power steering issue, and I kept saying "park the car with the nose pointed down a hill overnight to reproduce the problem." They finally said "ohh, only when it's parked on a hill" (and they had been told that a dozen times over six months of trying to address the issue.
Their comback: "Umm, we don't have a hill, so I guess we're out of luck."
I offered to let them borrow my floor jack and a block of wood.
After six months of botching -- they finally realized after all the power steering parts they had switched out (often installing wrong parts,) they had NEVER bled the power steering system once. AIR BUBBLES!!!!!!
The perception that Jaguar's quality has improved is mostly based on initial perception, but long term ownership experience still supports that Jags (like almost all Ford, GM and Chrysler-owned vehicles) are complete piles of poorly engineered junk.
Interestingly, the accepted bottom line in quality is that automotive issues are no longer due to bad workmanship, but are engineered into (or not engineered OUT) a specific vehicle system. Automakers send cars out with known problems, but it's less expensive to fix under warranty than redesign. Hence, why Chrysler/Dodge trannies always break, Caddy tranny electronics always malfunction, why Corvette fuel gauges get "contaminated," and all GM 3800 V6 engines will need a new intake within 150,000 miles (usually closer 50K, though.)
I'm rambling ... Sorry!