That's the point, lab test mean nothing in the field, you have to shoot over a period of time in the conditions to see if the equipment does what you need. You will soon see if a lens doesn't perform as you need or a camera handles well enough etc A lab test just shows it can take pictures of a chart bracket focused on a tripod etc no real indicator how it produces the goods at a sporting event, wedding, fashion shoot or the Zoo. The net has produced a plethora of mathematicians that decide wether a lens or camera works or not by producing charts and statistics and seldom pictures of anything of note. It's like deciding on a car by the 0-60 mph time. At best a chart will show that a lens camera combination isn't a complete dogs dinner.
They might mean nothing to you, but they are meaningful to me. Below are a couple of charts from Photozone comparing the performance of the Canon EF-S 17-55/F2.8 zoom with the highly regarded Canon 50/F1.4 prime.
These charts are only an indirect indicator of lens performance. They are more correctly an indicator of 'system' resolution. The camera used was the 8mp Canon 350D, so the results should be relevant for owners of cameras with a similar pixel density, such as the 20D, 40D and 1Ds3 (in the case of the 50/1.4), although there's no information here about the edge performance of the 50/1.4 on the 1Ds3.
The above charts only describe the performance of the lenses at 50% MTF. The choice of the 50% figure appears to be based upon subjective factors in relation to real world images. Lenses which deliver a high resolution at 50% contrast tend to produce real world images that look sharp and detailed. Performance at 30% MTF (for example) would be less relevant to an appearance of sharpness because such low contrast signals tend to get buried in noise, unless one is shooting high contrast line charts, or unless one's real world images contain image components similar to lines charts, such as street signs, advertising billboards, tree branches against a light background, shop signs etc.
Examining these bar charts, one should notice something quite remarkable. The EF-S zoom appears to be as sharp as the 50mm prime, across the apertures they both have in common, ie. from F2.8 to F8. My decision to buy this zoom was sparked by the sight of this chart comparison.
Unfortunately, the circumstances in the small store in a busy shopping centre in Bangkok (where I bought the lens) were not conducive to my testing the lens thoroughly before buying. But later testing has confirmed that this lens is indeed as sharp as my copy of the 50/1.4 prime, and just like the charts indicate, is not quite as sharp at the edges of the frame as the 50mm prime which is, of course, designed for a larger format.
However, one factor which the charts do not (and cannot) address is autofocussing accuracy. I'm disappointed with the autofoussing capability of this lens, even after calibration by Canon back home in Australia.