'Style', i think is the approach used in teaching aikido by the senseis. you see, this is the unique part of aikido. Aikido, as far as I know, is a flexible martial art that leaves the practitioner to practice what they think is most comfortable for them. For example, Shioda sensei wants to preserve O'Sensei teachings like he used to learn so that Yoshinkan was formed. Even in the Aikikai itself many senseis have different method and approach of teaching.
But as Joe Thambu sensei said, don't look for differences because usually differences keeps you away from each other, look for similarities because from that you can exchange each other. An ikkyo is still form like ikkyo although people call it ikkyo, ikkajo, oshi taoshi, etc.