Should I be suspicious of someone who always stays friends with her exes?

I'm beginning a relationship with a 26 year old woman who is friends with all four of her ex-boyfriends who she's had serious long-term relationships with/has been in love with. This seems a little odd to me--she says they're all platonic, but I don't really see the point in staying friends with exes, and it seems like if she's loved them and had ual relationships with them, it's hard to believe that these "friendships" can be and/or remain platonic.