Zabbix 1.4 does a check for php-bcmath when going through the initial frontend instalation. I have not checked 1.4.1 for this yet. At least FC6, F7 and RHEL5 has php-bcmath as a separate package, so the zabbix-web subpackage should have "Require: php-bcmath".
Hm... You mentioned zabbix 1.4.1... I don't see that mentioned anywhere on the zabbix site, or were you referring to in-development code? In either case, I'm pushing a new zabbix package that does include the R: php-bcmath for zabbix-web.
Yes, I am talking about 1.4.1 branch in subversion, which should be published really soon.
zabbix-1.4-3.fc7 has been pushed to the Fedora 7 stable repository. If problems still persist, please make note of it in this bug report.