John there is a lot of misinformation here.

First I am not a "brand loyalist"- I have recent MOTL boards from Korg, Roland, and Yamaha. And I have created custom styles on all three. I also have the old RA-800 (which has the features of the G-800 in a module), and a Yamaha QY-100 stand-alone sequencer. I rarely find the need to use either.

Roland does have a "piano roll editor" and has some handy functions to substitute drum sets, etc. But by and large the style composer is NOT as sophisticated as Korg's or Yamaha's. For example, you cannot specify whether the arranger should retrigger a sustained note on the accompaniment track if the chord is released and played again later in the measure. K and Y both allow you to specify this. Just look at the number of pages in the manual devoted to style creation and you will see that Korg and Yamaha have put a lot more thought into it (Look up NTT, NTR, RTR, etc. Roland has the "Alteration" parameter but that's about it.)

The Korg is very flexible but it took me a while to get my head into their operating system. For example, Korg allows you to have different style patterns for six different types of chords. However it is not required to make the pattern different for each type of chord. Generally the Korgs (beginning with the addition of the "fixed" interval type on the PA-800) matches or exceeds the Yamaha feature for feature in style creation.

On the Tyros, you can definitely delete an accompaniment and re-record it from scratch. You can also modify the bass line. However you cannot do this and re-save it as a FACTORY style. What you can do, is copy the factory style to a user style. Then you can to whatever you want. You can even "morph" styles-- build a custom user style by taking the rhythm from one factory style and combining it with the bass line from another, etc. Then you can still edit the resulting product.

There are certain functions the Yamaha sequencer lacks, and it is true that some special style features (such as a different intro for a minor chord) are only accessible by using a 3rd party "CASM" editor on your PC. But I have done this and it's not difficult.

Everyone is entitled to his own opinion, but just because something is posted on the Internet doesn't mean it's true! When in doubt, download the manuals, or go to a nearby store and see for yourself what can be done. Most of these boards are so deep, it's not a question of "whether" it does something, but "how".
Hope this helps,
Ted

Edit: Although I have not used one, based on the manual, it appears that the Ketron SD5 is also quite flexible in creating and customizing styles. -Ted

[This message has been edited by TedS (edited 06-18-2010).]