Compared to indian style toilets, western toilets are comfortable but cleanliness-wise, worst because using it involves the resting of thighs on the commode which is mostly unclean.
Though after use, taharah can be regained by washing the thighs, it is not practical to do it with pants (izaars or bottoms) on and hence ghusl could be preferred.
Performing ghusl after use is also not practical when he is outside home (trains, flights, etc.). How then would a Muslim use the western toilets and regain taharah without ghusl?
This question is very important because these days all toilets in trains, flights and hotels are being westernised.