I seem to remember spammers doing this in order to evade naive spam filters. For example, substitute "v1agra" for "viagra", and get through to the inbox. Though

I seem to remember spammers doing this in order to evade naive spam filters. For example, substitute "v1agra" for "viagra", and get through to the inbox. Though once you use a trick like that and it gets marked as spam a few times, you can't use it again. So yeah, perhaps your reason is more sensible.