why not use memset to clear each struct content in dvb-app?

Dear all:
In dvb-app, like en50221_app_mmi.c, we will call
en50221_app_mmi_create to create mmi struct.
my question is why we use below assignments
	mmi->funcs = funcs;
	mmi->closecallback = NULL;
	mmi->displaycontrolcallback = NULL;
	mmi->keypadcontrolcallback = NULL;
	mmi->subtitlesegmentcallback = NULL;
	mmi->sceneendmarkcallback = NULL;
	mmi->scenecontrolcallback = NULL;
	mmi->subtitledownloadcallback = NULL;
	mmi->flushdownloadcallback = NULL;
	mmi->enqcallback = NULL;
	mmi->menucallback = NULL;
	mmi->listcallback = NULL;
	mmi->sessions = NULL;
instead of using memset(mmi, NULL, sizeof(struct en50221_app_mmi);
thanks for your help,
miloody