I don't know where the "express" fast bowlers have gone though it has alot to do with the workload and types of games played.
As mentioned above Thomson and Holding were out of this planet. Thommo was frightening at his peak and there is no way any of those "official" timings of Akhtar, Tait or Lee were faster than Thomson. Thommo himself reckons he clocked nearer 180kph than 160kph (now we jump at a ball of 145kph). He was a naturally superb athlete.
Thommo bowled deliveries that would bounce over the keeper and hit the sight screen on the full. Marsh would stand halfway to the boundary. Some deliveries you just didn't see. Holding was close in pace but his natural action was less scary.
Plus, Thommo was a khunt who enjoyed hitting blokes on the scone. Great days.