Common sense is that: if your company(site) is big or famous, you should put site title after page title. You can see this kind phenomenon on sites like IBM, ORACLE and so forth.
Some small companies (web sites)but famous in their market niches also do this.
In addition to that, if some small companies want to push hard on their brands, they also put their site names before page titles.
That being said, I do not believe there is much difference in terms of SEO or accessibility, if any. The thing you need to care about, regarding to SEO, is keepping page tile unique and putting some keywords to it. Also, keep it constant by putting either site titles behind or page titles behind for all of your page.