i've noticed this too... on many occasions i've refrained from typing something because when read as it is, it sounded offensive and could have hurt the other person's feelings. But when i say the same thing, it can be taken in a joking manner.
The problem lies with the absence of speech vectors while typing. We can still emphasize some things by making the text bold or with emoticons, but it is not sufficient. Speech vectors enables a speaker to communicate efficiently.
E.g. Try the different way you can use/say f***k in various situations....The sentence is the same but with the correct tone, the meaning changes---
What the f***k? (Horror)
What the f***k? (disbelief)
What the f***k? (question)
Now, if anyone was to read this without the situations in the brackets, they all would appear the same. Hence the skills required for internet communication have to be honed over time. The typing thing also limits the use of speech vectors. So, one needs to come up with sentences that puts the point across (the correct one, that is) and does not sound offending when read.
Just my two cents
BSK