Judging by the review of these apps in the Windows Phone Store some user have been experiencing bugs, most notably in the Ringtone Maker app. By offering prompt updates Nokia should help offset the majority of consumer concern this generates.
Nokia has made it clear on multiple occasions that it believes that publishing its own exclusive apps and licensing apps exclusively for Nokia devices from third parties is an important way of making it devices stand out from its competitors, both within the Windows Phone platforms, but also more generally in the smartphone space. However, the effort can also be seen as the consequence of the need to fill gaps in both the core platform offering and the app listings of the Windows Phone Store itself.
In practise Nokia's app strategy is a result of a combination of these factors. It's fair to say that Nokia is investing in apps because of Windows Phone's relative weakness compared to Android and iOS, but at the same time it's important to realise that a significant proportion of the effort would be happening regardless of the state of the "third party" app ecosystem.