Based on what I learned during my international management courses, I think it's just a matter of cultural differences. In general American companies are more in to your face when they want to promote a new product. They bring it as it's the best thing on the market, beats the competition, they highlight it's unique features and try to convince potential customers that it's exactly what they need. They are very expressive.
Japanese are the complete opposite. They are passionate about their product and are very dedicated. They're afraid to lose face and don't want to disappoint others, hence the famous delays of all the GT games. Big talk isn't accepted in their culture. They have a saying 'only dead fish have an open mouth', comparable to the English 'empty vessels make the most noise'. I think that's one of the reasons Kazunori negates Turn 10's accomplishments, simply because he condemns their attitude.