Why regexp works different in stock vi vs. vim

[Артур Истомин]

I have file where first symbols are tabs:

        Sally tried really really hard
                Timmy tried really really really hard
                        Johnny tried really really really really hard

When I search tabs in stock vi with '/\t'. It finds all words 'tried'. In
vim it finds tabs. Why? In fact, I can't find tabs in stock vi anyhow.My 
system is OpenBSD 5.8

Thanks.