The Society for Music Theory (SMT) sponsors an email list, smt-list, for people interested in discussing theoretical issues about music. It is primarily of and for professional music theorists, but there are some other musicians and interested amateurs as well. While the list is typically very quiet during the summer, currently there is a discussion ensuing about the nature of scales.
Coming out of a discussion about whether music does or can have a syntax, the new thread focuses on whether diatonic scales naturally prioritize specific notes to be the tonic. Jay Rahn argues that in a white note collection (C D E F G A B) that uses triads as the main harmonic referents, C or A will have a head start over other notes in being heard as tonic. One suggested reason for this priority is that the C major triad and the A minor triad are the only triads of this diatonic collection that do not contain a note a tritone away from another note of the collection. In this collection, B and F form the tritones, so any triad with B or F would not be prioritized to be tonic. This explanation is attributed to Godfrey Winham.
Dmitri Tymoczko disagrees with the concept that diatonic scales will naturally gravitate towards certain notes as tonic, and also feels that symmetric collections like the whole tone scale or octatonic scale can be used to create a sense of tonic just as easily as diatonic scales.
I agree with Dmitri that the context determined by the composer is much more important in determining what note is prioritized than the intervallic content of the collection or scale. But I can also see that asymmetric scales can help to serve as guide posts in the perception of tonic. I don't think C or A have a head start on being perceived as tonic in the white note diatonic collection, so lets assume that the composer has written music with F as the tonic note. There are only two half steps in the diatonic scale, in this case between scale degrees 4 - 5 and 7 - 1. Thus any time a half step is heard, the listener will easily identify it as being one of those two locations. The first half step is preceded by two whole steps, the latter by three, so hearing three whole steps in a row is also a guidepost. With symmetric scales, there are no unusual features to help the listener. Locating your place in the scale in relation to tonic is like finding a house in a cookie cutter housing division. It is possible, but all the houses look the same, so you had better remember the address and the directions. With the diatonic scale, each house looks quite different, and there is only one street to drive down (maybe two).