This should help you out. Write data to file (changed cut -c5- to cut -c4- because it was deleting the first digit):
wget -O - -o /dev/null http://www.stackoverflow.com/ | cat | sed "s/</\n</g" | grep '<\/\{0,1\}[a-zA-Z][a-zA-Z\:\._\-]\{0,\}' | cut -f 2 -d"<" | cut -f 1 -d">" | cut -f 1 -d" " | sed "s/\//\\n/g" | sort | uniq -c | tail -n +2 | cut -c4- > mydata.txt
Create myplot.dem (some custom initialization added here, change it as you like it):
set style data histogram
set style fill solid border -1
set log y
set boxwidth 0.9
set term png
set tics out nomirror
set xtics rotate by -45
set output "histogram.png"
plot "mydata.txt" using 1:xticlabels(2)
and finally:
gnuplot myplot.dem
creates your plot "histogram.png" in current directory.