Here's the deal with the Bertini M5: you'll have to purchase the adaptor bar as an accessory for around $25 extra.
Regarding your questions: I don't know that it's truly a drawback that Bertini has no (pre-installed) infant carrier adaptor. For about the first three months of your child's life you will feel that the infant carrier to stroller transition (and back) is lovely and convenient. Around the fourth month you will probably be grunting to put the carrier in or out of the stroller as your child will really be gaining weight at that point-- and will be crossing over from an infant carrier sometime soon.
It's a matter of personal preference though-- for $25 you can stick most any infant carrier in the M5 and be good to go. Another way to think of it: the added infant carrier convenience for those 3-4 "light-baby" months would be cost you about $7-8 extra per month.
If you want to purchase the adaptor just check this link at baby universe:
bertini car seat adaptor
They also sell the M5 for $299.00.
If you want more information about the M5, you can always read our review:
http://strollers.baby-gaga.com/bertini-m5.php
Personally, it's one of my favorite strollers on the market, and I think the travel system concept is a bit over-rated. (That's my opinion, some parents love it).
Good Luck!
Mara