There have been four bowlers who've averaged under 27, and six who've averaged between 27 and 30, in Tests against Test-class teams, with a qualification of 500 overs bowled.
These bowlers are:
Muttiah Muralitharan (average of 19.66 in 37 games - could almost certainly be more if SLC had played less against Bangladesh though)
Shoaib Akhtar (22.08 in 24 - missing 21 in that time)
Glenn McGrath (22.34 in 46)
Shane Warne (24.76 in 50)
Shaun Pollock (27.70 in 47)
Makhaya Ntini (28.47 in 58)
Chaminda Vaas (28.70 in 41)
Jason Gillespie (29.55 in 40)
Anil Kumble (29.89 in 51)
Harbhajan Singh (29.92 in 37)
Two of these are still playing and could very easily go over 30 with just a few runs.
Now, clearly this is not an exhaustive nor all-telling list: Vaas, as we all know, can go from brilliant to innocuous with no warning; Pollock was far better last season than at any point since 2000\01 (and has promptly been dropped...); and Ntini blows almost as hot-and-cold as Vaas, though with some element of a pattern there unlike the Lankan. Also, Andrew Flintoff since December 2003 has averaged 28.36 in 38 after going from hopeless to good. What's more, there are at least a couple of bowlers (Mohammad Asif and Stuart Clark) who are very likely to soon break into the qualification requirements, and a few other promising bowlers hovering just over 30 (James Franklin, Matthew Hoggard, Umar Gul, Andre Nel, Laaasith Maaalinga).
Nonetheless, this, more than any statistic regarding batting-average, runs-per-match, run-rate, etc. shows how bat has dominated ball in the time in question. Blame poor (flat) pitches, blame poor cricket-balls, blame lack of good bowlers, blame all three, heck even blame better batsmen if you must (denial of reality IMO).
But the fact that just three bowlers (two of whom are wristspinners) have truly convinced in the last 6 years, while 1 other has retained consistency and respectibility, tells one hell of a lot.