<p>Why doesn't this Google Chart API URL render both data sets on this XY scatter plot?  </p>

<pre><code>http://chart.apis.google.com/chart?cht=lxy&amp;chd=t:10,20,30,40,50,60,70,80,90,100,110,120,130,140,150,160,170,180,190,200|0.10,0.23,0.33,0.44,0.56,0.66,0.79,0.90,0.99,1.12,1.22,1.33,1.44,1.56,1.68,1.79,1.90,2.02,2.12,2.22|0.28,0.56,0.85,1.12,1.42,1.68,1.97,2.26,2.54,2.84,3.12,3.40,3.84,4.10,4.53,4.80,5.45,6.02,6.40,6.80&amp;chco=3072F3,ff0000,00aaaa&amp;chls=2,4,1&amp;chs=320x240&amp;chds=0,201,0,7&amp;chm=s,FF0000,0,-1,5|s,0000ff,1,-1,5|s,00aa00,2,-1,5
</code></pre>

<p>I've read the <a href="http://code.google.com/apis/chart/" rel="nofollow noreferrer">documentation</a> over and over again, and I can't figure it out.</p>

I think it actually does render both data sets, but you can only se one of them because there's only one scale on the y axis. (In other words, 0.10 is too small to show.)
And, you should really be using percentages. 100 is the highest accepted value:
Where chart data string consists of positive floating point numbers from zero (0.0) to one hundred (100.0)