I think he is overdoing this. Too much watering down can lead to a decline in the brand image. He doesn't want to be the Next ralph lauren or Tommy hilfiger.
Although it certainly looks like it, he better not want something like that to happen! Ralph and Tommy are brands that built a finantial-"empire" doing basics, kids-stuff, average clthes, outlets... (which seconds what
luxx and
ilauhead have mentioned before)
he can't just send down the runway 50 girls on wicked shoes and concordes in their heads, and pretend to grow and reach everyone in the big market!
The big american companies (or armani in italy) have all a cohesive brand image, and there's always similarities between the different lines.
You can certainly dilute your prices a bit in second and third lines, but if you also start to water down your ideas and aesthetic, you may end up with the kind of snob arguments
alejandro mentioned (which doesnt benefit either lines)
You may wanna be the next Ralph Lauren, but you have to know that has some very serious costs in terms of creativity/brand image...
and when the interests in profit are so much more important than these costs, maybe you should consider calling yourself a designer.
on a side note: i would NOT like to see a Givenchy second line... thinking of it just makes me

... in general, i wouldnt like to see second lines of any french house (Maybe just capsule collections like 24 chez Saint Laurent, which i think is a totally different concept)