I find that to be confusing. One of the points of the meta tag is to have the content type so that the specification of the page is known, think syntax checking or even at times type checking. reply_html_page/2 makes some knowledge of the content type.
So I am thinking that if there is no content type then reply_html_page/2 should not be used and something at a lower level from SWI-Prolog should be used in constructing the response. 
If that is the case then also should not an entire Prolog module be created similar to reply_html_page/2 that knows of the specifics of the response needed for /fortunes? library(quasi_quotations): Define Quasi Quotation syntax comes to mind, See: Is there a way to go from HTML to the Prolog representation of the HTML?
The reason I state this is that in reading about html_set_options/1 with content_type(+ContentType) it seems that removing the meta tag for reply_html_page/2 is not something that should be done.
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?- html_current_option(Option).
ERROR: Unknown procedure: html_current_option/1 (DWIM could not correct goal)
?- use_module(library(http/html_write)).
true.
?- html_current_option(Option).
Option = dialect(html5) ;
Option = doctype(html) ;
Option = content_type('text/html; charset=UTF-8').