Music sightreading skill - practice doesn't make perfect

I have an ability to sightread extremely complicated and difficult music, a fact noted by my first piano teacher after my initial lesson when I was six years old. It seems obvious to me that I came wired that way, practice had very little to do with it. This attitude, which conflicts with the general view that expertise is due mainly to diligent and repetitive practice of a skill, is confirmed by recent observations of Meinz and Hambrick:

Deliberate practice—that is, engagement in activities specifically designed to improve performance in a domain—is strongly predictive of performance in domains such as music and sports. It has even been suggested that deliberate practice is sufficient to account for expert performance. Less clear is whether basic abilities, such as working memory capacity (WMC), add to the prediction of expert performance, above and beyond deliberate practice. In evaluating participants having a wide range of piano-playing skill (novice to expert), we found that deliberate practice accounted for nearly half of the total variance in piano sight-reading performance. However, there was an incremental positive effect of WMC, and there was no evidence that deliberate practice reduced this effect. Evidence indicates that WMC is highly general, stable, and heritable, and thus our results call into question the view that expert performance is solely a reflection of deliberate practice.